Biological role

1. TPP is involved in decarboxylation reactions of α-keto acids;

2. TPP is involved in the breakdown and synthesis of α-hydroxy acids (for example, ketosaccharides), i.e. in the reactions of synthesis and cleavage of carbon-carbon bonds in close proximity to the carbonyl group.

Thiamine-dependent enzymes are pyruvate decarboxylase and transketolase.

Avitaminosis and hypovitaminosis.

Beriberi disease, disorders of the digestive tract, changes in the psyche, changes in the activity of cardiovascular activity, the development of a negative nitrogen balance, etc.

Sources: vegetable products, meat, fish, milk, legumes - beans, peas, soybeans, etc.

Daily requirement: 1.2-2.2 mg.

Vitamin B2 (riboflavin, growth vitamin)

In addition to riboflavin itself, natural sources contain its coenzyme derivatives: flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These coenzymatic forms of vitamin B2 predominate quantitatively in most animal and plant tissues, as well as in microorganism cells.

Depending on the source of vitamin B2, it was called differently: lactoflavin (from milk), hepaflavin (from the liver), verdoflavin (from plants), ovoflavin (from egg white).

Chemical structure: The riboflavin molecule is based on a heterocyclic compound - isoalloxazine (a combination of benzene, pyrazine and pyrimidine rings), to which the pentaatomic alcohol ribitol is attached at position 9. The chemical synthesis of riboflavin was carried out in 1935 by R. Kuhn.

Riboflavin

Solutions of vitamin B2 are orange-yellow in color and are characterized by yellow-green fluorescence.

Yellow color is inherent in the oxidized form of the drug. Riboflavin in reduced form is colorless.

B2 is highly soluble in water, stable in acidic solutions, easily destroyed in neutral and alkaline solutions. B2 is sensitive to visible and UV radiation, easily undergoes reversible reduction, adding H2 at the double bond site and turning into a colorless leuco form. This property of vitamin B2 to be easily oxidized and reduced is the basis of its biological action in cellular metabolism.

Avitaminosis and hypovitaminosis: stunting, hair loss, inflammation of the mucous membrane of the tongue, lips, etc. In addition, general muscle weakness and weakness of the heart muscle; clouding of the lens (cataract).

Biological role:

1. It is part of the flavin coenzymes FAD, FMN, which are prosthetic groups of flavoproteins;

2. Participates in the composition of enzymes during direct oxidation of the initial substrate with the participation of O2, i.e. dehydrogenation. The coenzymes of this group include oxidases of L- and D-amino acids;

3. As part of flavoproteins, electrons are transferred from reduced pyridine coenzymes.

Sources: yeast, bread (coarse flour), cereal seeds, eggs, milk, meat, fresh vegetables, milk (in the free state), liver and kidneys (as part of FAD and FMN).

Daily requirement: 1.7mg.

Vitamin B6 (pyridoxine, antidermic)

Opened in 1934 by P. Györdi. First isolated from yeast and liver.

Chemical structure . Vitamin B6 is a derivative of 3-hydroxypyridine. The term "vitamin B6" on the recommendation of the International Commission on the Nomenclature of Biological Chemistry refers to all three derivatives of 3-hydroxypyridine with the same vitamin activity: pyridoxine (pyridoxol), pyridoxal and pyridoxamine.

pyridoxine pyridoxal pyridoxamine

B6 is highly soluble in water and ethanol. Aqueous solutions are very resistant to acids and alkalis, but sensitive to light in the neutral pH zone.

Avitaminosis hypovitaminosis. In humans, vitamin B6 deficiency manifests itself in inhibition of the production of red blood cells, dermatitis, inflammatory processes of the skin, slowing down the growth of animals, impaired tryptophan metabolism.

biological role. All three derivatives of 3-hydroxypyridine are endowed with vitamin properties, coenzyme functions are performed only by phosphorylated derivatives of pyridoxal and pyridoxamine:

pyridoxamine phosphate pyridoxal phosphate

Pyridoxamine Phosphate as a coenzyme, it functions in the reactions of the conversion of carbonyl compounds, for example, in the reactions of the formation of 3,6-dtdeoxyhexoses, which are included in antigens localized on the surface of bacterial cells.

Biochemical functions pyridoxal phosphate:

1. transport - participation in the process of active transfer of certain amino acids through cell membranes;

2. catalytic - participation as a coenzyme in a wide range of enzymatic reactions (transamination, decarboxylation, racemization of amino acids, etc.);

3. the function of the regulator of the rate of turnover of pyridoxal enzymes is the prolongation of the half-life in the tissues of some pyridoxal apoenzymes when they are saturated with pyridoxal phosphate, which increases the resistance of apoenzymes to thermal denaturation and the action of specific proteinases.

With vitamin B6 deficiency, disturbances in the metabolism of amino acids are observed.

Sources: in products of plant and animal origin (bread, peas, beans, potatoes, meat, liver, etc.). It is also synthesized by the intestinal microflora !

Daily requirement: about 2 mg.

Vitamin B12 (cobalamin, antianemic)

Cobalamins are a group name for compounds with B12-vitamin activity.

Chemical structure. The central part of the vitamin B12 molecule is a cyclic corrin system, resembling porphyrins in structure (they differ from them in that two pyrrole rings are tightly condensed with each other, and not connected through a methylene bridge). Under the plane of the corrin ring, in the center of which is Co, there is a residue of 5-deoxyadenosine attached to cobalt.

Avitaminosis and hypovitaminosis. A lack of vitamin B12 leads to the development of pernicious anemia, disruption of the TSNS activity and a sharp decrease in the acidity of gastric juice.

For the active process of absorption of vitamin B13 in the small intestine, a prerequisite is the presence in the gastric juice of the internal factor of Castle (a special protein - gastromucoprotein), which specifically binds vitamin B12 into a special complex complex and is absorbed in the intestine in this form.

biological role. Enzyme systems have been identified, which include cobalomide coenzymes as a prosthetic group.

chemical reactions, in which vitamin B12 takes part as a coenzyme, is conventionally divided into two groups. The first group includes transmethylation reactions, in which methylcobalamin acts as an intermediate carrier of the methyl group (reactions for the synthesis of methionine and acetate).

The second group of reactions involving B12-coenzymes is the transfer of hydrogen in isomerization reactions.

Sources: meat, beef liver, kidneys, fish, milk, eggs. The main place of accumulation of vitamin B12 in the human body is the liver, which contains up to several mg of the vitamin.

Vitamin B12 is the only vitamin whose synthesis is carried out exclusively by microorganisms.

Synthesized by intestinal microflora !

daily requirement 0.003 mg.

Biochemistry, its tasks. The value of biochemistry for medicine. Modern biochemical research methods.

BH is the science of the structure of substances that make up a living organism, their transformations, and the physicochemical processes that underlie life.

BC tasks

1.Study of BIOCATALYSIS processes.

2. Study of the mechanisms of heredity at the molecular level.

3. Study of the structure and metabolism of nucleic acids.

4. Study of the structure and metabolism of proteins, fats

5. Study of the conversion of carbohydrates.

7.Study of the biological role of signaling molecules (HORMONE).

8. Study of the role of vitamins in metabolism.

9. Study of the role of minerals.

The value of HD for medicine.

The main tasks of medicine: pathogenesis, diagnosis, treatment, prevention of diseases.

1. Significance of HD for understanding the mechanism of the disease.

ETC. Cardiovascular diseases(atherosclerosis). It is now assumed that the sensitivity of cell receptors to LDL is important.

2. Significance of HD for the diagnosis of diseases.

Widespread use of biochemical studies of biological fluids.

A. Number of substrates.

B. Study of enzyme activity.

B. Study of hormone levels. Methods RIA, ELISA. Identification of PREDISEASES.

3. Significance of HD for treatment. Identification of disturbed metabolic links, creation of appropriate drugs, widespread use of natural drugs.

4. Importance of HD for disease prevention. ETC. The lack of vit. C -scurvy - for the prevention of vit. C. Deficiency of vit. D-rickets-vit. D

Amino acids, their classification. The structure and biological role of amino acids. Chromatography of amino acids.

Proteins are made up of AA. All AKs can be divided into 4 groups:

1 .Interchangeable - synthesized in the body: ALA, ASP, ASN, GLU, GLN, GLI, PRO, SER.

2. Irreplaceable - are not synthesized in the body and come with food: VAL, LEY, ILE. LIZ. TRE, MET, FEN, THREE.

3. Partially replaceable - synthesized in the body, but very slowly and do not cover all the needs of the body: GIS, ARG.

4. Conditionally replaceable - synthesized from essential amino acids: CIS (MET), TIR (FEN).

The completeness of protein nutrition is determined by:

1. The presence of all essential amino acids. The absence of even one essential amino acid disrupts protein biosynthesis.

1. Amino acid composition of the protein. All AAs can be found in products of both animal and plant origin.

In the isoelectric state, the protein is less stable. This property of proteins is used in their FRACTION:

1. ION EXCHANGE CHROMATOGRAPHY.

For it, ION EXCHANGERS are used, which are made from pure cellulose: DEAE - cellulose (contains cationic groups); KM - cellulose (contains anionic groups). Negatively charged proteins are separated into DEAE, positively charged proteins into KM. The more COOH groups in a protein, the more strongly it binds to DEAE cellulose.

2. Separation of proteins based on the magnitude of the charge - protein electrophoresis. With the help of electrophoresis in the blood serum, at least 5 fractions are isolated: ALBUMIN, alpha, alpha-2, gamma, beta - globulins.

Principles of protein classification. characterization of simple proteins. Characterization of histones and protamines.

Coenzymes and their functions in enzymatic reactions. Vitamin coenzymes. Examples of reactions involving vitamin coenzymes.

COFERMENTS - low molecular weight organic substances of non-protein nature. They most often contain various vitamins in their composition, therefore, they are divided into two groups: 1. Vitamin. 2.Non-vitamin.

1. THIAMINE in the composition of vitamin B1 (THIAMIN) - TMF - THIAMIN MONOPOSPHATE, TDF - THIAMIN DIPHOSPHATE, TTP - THIAMIN TRIPHOSPHATE. TPP is associated with enzymes alpha KETOACID DECARBOXYLASES (PVA, alpha KGC)

2. FLAVIN contain vitamin B2 - FMN - FLAVINMONONUCLEOTIDE, FAD - FLAVIADENNINDINUKLEOTIDE.

FMN and FAD are associated with dehydrogenase enzymes. Participate in dehydrogenation reactions.

3. PANTOTHEIN (vitamin VZ) - KOF A (HS-KOA - HS COENZYME A) - acylation coenzyme.

4. NICOTINAMIDE contain vitamin PP (NIACIN) - OVER (NICOTINAMID Adenine Dinucleotide), NADP (NICOTINAMID Adenine Di Nucleotide Phosphate). Associated with DEHYDROGENASES:

5. PYRIDOXINE contain vitamin B6. PAF - PYRIDOXAMINOPHOSPHATE, PF - PYRIDOXALPHOSPHATE.:

1. TRANSAMINATION reactions (TRANSAMINATION). Associated with enzymes aminotransferases.

2. AC DECARBOXYLATION REACTIONS.

Nomenclature and classification of enzymes. Characteristics of the class of oxidoreductases. Examples of reactions involving oxidoreductases

1. OXIDOREDUCTASES.

2. TRANSFERASES.

3. HYDROLASES.

5. ISOMERASES.

6. LIGASES.

Each class is divided into subclasses. Sub-classes are divided into SUB-CLASSES.

1. OXIDOREDUCTASES.

Enzymes of this class are involved in OVR. This is the most numerous class of enzymes (more than 400 OXIDOREDUCTASES). 1. AEROBIC DEHYDROGENASES. They participate in DEHYDROGENATION reactions.

Some AEROBIC DEHYDROGENASES are called OXIDASES. For example, OXIDASE AK.

2.ANAEROBIC D D. These enzymes are also involved in DEHYDROGENATION reactions, i.e. removal of H2 from the oxidized substrate and its transportation to any other substrate, except for O2.

3. PEROXIDASES. Enzymes that take H2 from the oxidized substrate and transport it to PEROXIDE.

4.CYTOCHROMES. They contain GEM. CYTOCHROMES are involved in the transport of only electrons.

Characterization of the class of lyases, isomerases and ligases (synthetases), examples of reactions.

2. Enzymes that break bonds between carbohydrate atoms in a non-HYDROLYTIC way without the participation of water (ALDOLASE).

3. Enzymes involved in the reactions of HYDRATION and DEHYDRATION.

ISOMERASES. Enzymes of this class are involved in isomeric transformations. In this case, one structural isomer can turn into another, due to intramolecular rearrangement of atoms.

LIGASES. Enzymes of this class are involved in the reactions of combining two or more simple substances with the formation of a new substance. These reactions require external energy in the form of ATP.

Characteristics of the enzyme classes of transferases and hydrolases. Examples of reactions involving these enzymes.

TRANSFERASES. Enzymes of this class are involved in the transport of atomic groups from the donor to the acceptor. Depending on the transferred groups, TRANSFERASES are divided into several subclasses:

1.AMinotransferase. They are involved in TRANSAMINATION reactions.

ASAT - ASPARAGINE AMINOTRANSFERASE.

2. METHYL TRANSFERASES (SNZ groups).

3. PHOSPHOTRANSFERASES (PHOSPHATE groups).

4. ACIL TRANSFERASES (acid residues).

HYDROLASES. Enzymes of this class are involved in the reactions of breaking bonds in substrate molecules with the participation of water.

1.ESTER ASES act on COMPOUND-ETHER bonds. These include lipases, phospholipases, cholesterases.

2. GLYCOSIDASE - acts on the GLYCOSIDA bond found in complex carbohydrates. These include AMYLASE, SUCHARASE, MALTASE, GLYCOSIDASE, LACTASE.

3.PEPTIDASES are involved in breaking PEPTIDE bonds in proteins. These include PEPSIN, CHIMOTRYPSIN, AMINOPEPTIDASE, CARBOXYPEPTIDASE, etc.

12. Modern ideas about the mechanism of action of enzymes. Enzymatic reaction steps, molecular effects, examples.

MECHANISM OF ENZYME ACTION. From a thermodynamic point of view, the action of any enzyme is aimed at lowering the activation energy. The lower the activation energy, the higher the reaction rate. The theory of enzyme action was proposed by BEILIS and VANBURG. According to it, an enzyme is a "sponge" that adsorbs molecules of reactants on its surface. It sort of stabilizes them, promotes interaction. 70 years ago another theory was proposed by MICHAELIS and MENTEN. They put forward the concept of the F-S complex. The enzyme interacts with the substrate, forming an unstable intermediate F-S complex, which then decomposes with the formation of reaction products (P) and the release of the enzyme. There are several stages in this process:

1. Diffusion of S to F and their STERIC interaction with F-S formation complex. This stage is not long. At this stage, there is practically no decrease in the activation energy.

2. Transformation of the F-S complex into one or more activated complexes. This stage is the longest. In this case, the bonds in the substrate molecule are broken, and new bonds are formed. E activation¯

3. The release of reaction products from the enzyme and their entry into the environment.

MOLECULAR EFFECTS OF ENZYMATIVE ACTION.

1. The effect of concentration. Therefore, the main role of enzymes is to attract the molecules of the reacting substances to their surface and the concentration of these molecules in the region of the active center of the enzyme.

2. Effect, convergence and orientation. The contact sites of the active site of the enzyme bind specific substrate molecules, bring them closer together, and provide orientation in a way that is beneficial for the action of the catalytic groups of the enzyme.

3. The effect of tension ("rack"). Prior to the attachment of the substrate to the active site of the enzyme, its molecule is in a relaxed state. After binding, the substrate molecule is stretched and takes on a stressed deformed configuration. Decreases E activation.

4. Acid-base catalysis. Acid-type groups split off H+ and have a negative charge. Basic type groups add H+ and have a positive charge. This leads to a decrease in the activation energy.

5. Effect of induced correspondence. It explains the specificity of the action of enzymes. There are 2 points of view on this: A). FISHER hypothesis. According to it, there is a strict STERIC correspondence between the substrate and the active site of the enzyme. IN). KOSHLAND's theory of induced correspondence. According to her, the enzyme molecule is a flexible structure. After the binding of the enzyme to the substrate, the CONFORMATION of the active site of the enzyme and the entire substrate molecule changes. They are in a state of induced correspondence. It happens at the moment of interaction.

13. Inhibition of enzymes. Competitive and non-competitive inhibition, examples of reactions. Medicinal substances as enzyme inhibitors.

INHIBITORS. Enzymes are catalysts with controlled activity. It can be controlled by various substances. The action of the enzyme can be INHIBITIONED by certain chemicals - INHIBITORS. By the nature of the action, inhibitors are divided into 2 large groups:

1. Reversible - these are compounds that interact NON-COVALENTLY with the enzyme, thus forming a complex capable of dissociation.

2. Irreversible - these are compounds that can specifically bind certain functional groups of the active center of the enzyme. They form strong COVALENT bonds, so such a complex is difficult to destroy.

TYPES OF INHIBITION. According to the mechanism of action, the following types of INHIBITION are distinguished:

1. Competitive inhibition- inhibition of the enzymatic reaction caused by the action of inhibitors, the structure of which is very close to the structure of S, therefore both S and the inhibitor compete for AC F. and that compound binds to it. whose concentration in environment more. E+S-ES-EP

Many drugs act as competitive inhibitors. An example is the use of SULFANIL (SA). For various infectious diseases that are caused by bacteria, SA preparations are used. The introduction of SA leads to INHIBITION of the enzyme of bacteria that synthesize FOLIC acid. Violation of the synthesis of this acid leads to a violation of the growth of microorganisms and their death.

2.NON-COMPETITIVE INHIBITION-inhibitor and substrate have no structural similarity; the inhibitor does not affect the formation of the F-S complex; a triple ESI complex is formed.

Such inhibitors affect the catalytic conversion of the substrate. They can bind both directly to the catalytic groups of AC F, and outside AC F. But in any case, they affect the conformation of the active site. CYANIDES act as a non-competitive inhibitor. They bind strongly to the iron ions of CYTOCHROMOXIDASE. This enzyme is one of the components of the respiratory chain. Blocking the respiratory chain leads to instant death of the body. The action can only be removed with the help of REACTIVATORS.

3.SUBSTRATE INHIBITION- this is the inhibition of the enzymatic reaction caused by an excess of the substrate. In this case, an F-S complex is formed, but it does not undergo catalytic transformations, because makes the enzyme molecule inactive. The action of the substrate inhibitor is removed by reducing the concentration of the substrate.

4.ALLOSTERIC INHIBITION. ALLOSTERIC enzymes can have 2 or more protomer units. At the same time, one has a catalytic center and is called catalytic, and the other has an ALLOSTERIC center and is called regulatory. In the absence of an ALLOSTERIC INHIBITOR, the substrate attaches to the catalytic site and the usual catalytic reaction proceeds. When an ALLOSTERIC INHIBITOR appears, it attaches to the regulatory unit and changes the CONFORMATION of the enzyme center, as a result of which the activity of the enzyme decreases.

14. The concept of isoenzymes. Characterization of lactate dehydrogenase (LDH) and creatine kinase (CK) isoenzymes. Diagnostic role of KK isoenzymes. The use of enzymes in medicine. Enzymodiagnostics and enzyme therapy. Enzymopathology, examples.

Isoenzymes are a group of F-s that catalyze the same reaction, but differ in some physicochemical properties. They arose as a result of genetic differences in the formation of the primary structure of the enzymatic protein. Isoenzymes have strict organ specificity.

Determination of the activity of isoenzymes is of diagnostic value.

LDH(lactate dehydrogenase) has 5 isozymes, each of which is a tetramer. These F-you LDH differ in combination - H and M-type. In the liver and muscles, LDH-4 and LDH-3 predominate and are maximally active. In the myocardium, renal tissue, LDH-1 and LDH-2 are maximally active. In case of liver pathology, the activity of LDH-4, LDH-5 sharply increases in the blood serum.

KFK(CREATINPHOSPHOKINASE) - 0.16 - 0.3 mmol / l. Consists of 2 units: B (brain), M (muscles). CK-1 (BB, 0%, CNS) increases with deep severe damage (tumor, trauma, brain contusion). CK-2 (MB, 3%, myocardium) increases with myocardial infarction, heart injury. CPK-3 (MM, 97%, muscle tissue) increases with myocardial damage, prolonged pressure syndrome.

Enzymopathology- studies diseases associated with a violation of the activity of F. in the body, or their complete absence. For example, phenylketonuria: phenylalanine is converted into various products, but not into tyrosine - phenylPVK, phenyllactate. This leads to a violation of the physical capabilities of the body. Another example is the absence of histidase. This F. is involved in the conversion of histidine; its absence leads to the accumulation of hys in the blood and urine, which has Negative influence on all metabolic processes, mental and physical development is inhibited.

Enzymodiagnostics- determination of F. activity for diagnostic purposes. Organospecificity is the cornerstone of it F. Nr. alkaline phosphatase - specific F, characterizes the state of bone tissue. Its activity increases with rickets, obstructive jaundice. During various destructive processes, the integrity of the membranes of damaged organs is violated, and F. is released into the blood. Nr. myocardial infarction.

enzyme therapy- the use of various F in clinical practice for medicinal purposes. HP with low acidity - pepsin.

Cytochromes of the electron transport chain. Their functioning. The formation of water as the end product of metabolism.

CYTOCHROMES are HETEROPROTEINS. Their protein part is HEM, the structure of which is 4 PYRROL rings and an iron atom, which easily changes valency. May also include copper.

20. Ways of ATP synthesis. Substrate phosphorylation (examples). Molecular mechanisms of oxidative phosphorylation (Mitchell's theory). Uncoupling of oxidation and phosphorylation.

The process of ATP formation in the respiratory chain is oxidative phosphorylation. Due to the energy of electron transport in DC, ATP is formed from ADP and inorganic phosphate. Substrate phosphorylation is the process of ATP synthesis from ADP and phosphate due to the energy of the oxidized substrate in the cytoplasm of the cell. An example of substrate phosphorylation is the reaction:

The main provisions of Mitchell's theory:

1. The MITOCHONDRIAL membrane is not permeable to protons.

2. A proton potential is formed in the process of electron and proton transport.

3. The reverse transport of protons in the MATRIX is associated with the formation of ATP.

The process of electron transport takes place in the inner membrane. Protons are transported into the intermembrane space, and electrons move along the respiratory chain. The inner membrane is negatively charged from the side of the matrix, and positively from the side of the intermembrane space. During breathing, an ELECTRO-CHEMICAL gradient is created; concentration and potential difference. The electrical and concentration gradient constitutes the PROTONGUE force, which provides the force for ATP synthesis. There are proton channels in certain areas of the inner membrane. Protons can pass back into the matrix, with the resulting energy going to ATP synthesis.

Uncoupling of respiration and phosphorylation

Some chemical substances(protonophores) can transport protons or other ions (ionophores) from the intermembrane space across the membrane into the matrix, bypassing the proton channels of ATP synthase. As a result, the electrochemical potential disappears and ATP synthesis stops. This is the uncoupling of respiration and phosphorylation. As a result of uncoupling, the amount of ATP decreases, and ADP increases. Uncouplers are lipophilic substances that easily pass through the lipid layer of the membrane. This is 2,4-dinitrophenol, which attaches a proton in the intermembrane space and transfers it to the matrix.

transamination and decarboxylation of amino acids. Chemistry of processes, characteristics of enzymes and coenzymes. The formation of amides.

1). The main pathway for the conversion of amino acids in tissues is the TRANSAMINATION reactions - reactions between AMINO- and KETO ACIDS. These reactions are catalyzed by an enzyme, aminotransferase. All amino acids except LYS and TPE can undergo TRANSAMINATION. The most important are AT, whose amino group donors are ALA, ASP, GLU.

The role of TRANSAMINATION reactions:

1. are used for the synthesis of non-essential amino acids.

2. Is initial stage amino acid catabolism

3. As a result of TRANSAMINATION, alpha-KETO ACIDS are formed, which are included in GLUCONEOGENESIS.

4. Occur in different tissues, but most of all in the liver. Determination of AT activity is of diagnostic value in the clinic. With an excess of ALANINE or a lack of ASPARTIC K-YOU:

1. ALA + alpha-CHC ↔ GLU + PVC

2. GLU + PIE ↔ASP + alpha-CHC

Decarboxylation of amino acids, the role of vitamin B6. Formation of biogenic amines

2). DECARBOXYLATION reactions - the destruction of the COOH group with the release of CO2. At the same time, amino acids in tissues form biogenic amines, which are biologically active substances (BAS):

1. NEUROMEDIATORS (SERETONIN, DOPAMINE, GABA),

2. Hormones (ADRENALIN, NORADRENALIN),

3. Regulators of local action (HISTAMINE).

GABA is an inhibitory NEIROMEDIATOR. DOPAMINE is a NEIROMEDIATOR of excitatory action. It is the basis for the synthesis of ADRENALIN and NOR ADRENALIN.

HISTAMINE increases the secretion of gastric juice, therefore it is used in clinical practice for probing. It has a vasodilating effect, lowers blood pressure.

27. Deamination of amino acids. Types of deamination. Oxidative deamination. Indirect deamination of amino acids using tyrosine as an example.

DEAMINE - destruction of the NH2 group with the release of ammonia. The following types are possible in the body:

1. Recovery

2.HYDROLYTHIC:

3. Intramolecular:

These three types of DEMINING occur during decay.

4. Oxidative. Only GLU undergoes oxidative deamination.

Other amino acids also undergo oxidative deamination, but this pathway is indirect. It goes through the GLU and is called the INDIRECT OXIDATIVE DEAMINE process.

CARBOMOYL PHOSPHATE

Urea is formed only in the liver. The first two reactions of the cycle (the formation of CITRULLINE and ARGININOSUCCInate) take place in the MITOCHONDRIA, the rest in the cytoplasm. The body produces 25 grams of urea per day. This indicator characterizes the urea-forming function of the liver. Urea from the liver enters the kidneys, where it is excreted from the body as the end product of nitrogen metabolism.

Features of the exchange of purine nucleotides. Their structure and decay. The formation of uric acid. Gout.

For the biosynthesis of PURINE bases, the denunciations of atoms and atomic groups are:

Oxidation of uric acid - oxidation of PURINE NUCLEOSIDES.

Uric acid is the end product of the breakdown of purine nuclei.

The level of uric acid indicates the intensity of the breakdown of purine bases in body tissues and food.

DISTURBANCE OF NUCLEOTIDE METABOLISM. HYPERURICEMIA - an increase in the level of uric acid in the blood indicates an increased breakdown of nucleic acids or purine nucleotides (gout). The disease is genetically determined and has a family character. With gout, uric acid crystals are deposited in the articular cartilage, synovial membrane, and fiber. Severe acute mechanical gouty arthritis and nephropathy develop.

Genetic code

Modern ideas about the structural and functional organization of DNA: gene (structural, regulatory elements of DNA) and non-gene (tandem repeats, pseudogenes, mobile elements of DNA) regions. Main directions molecular biology(OMICS): genomics, transcriptomics, pH-omics.

95% of human DNA is non-genetic. 5% - the actual genes.

FUNCTIONAL ELEMENTS OF THE GENOME:

1. STRUCTURAL GENES

2. REGULATORY ELEMENTS

Structural genes encode the synthesis of mRNA, tRNA, rRNA. Regulatory elements do not encode RNA and, accordingly, proteins; affect work

structural genes.

The non-gene part is represented by:

1. TANDEM REPEATS monotonous repeats of NUCLEOTIDES that do not make sense. These are the so-called "desert regions" of DNA. At present, the meaning of these sites: the performance of a structural function and a site for the formation of genes in evolution (evolutionary reserve).

2. PSEUDOGENES - inactive but stable genetic elements resulting from a mutation in previously working genes (genes turned off by mutation). It is a by-product and genetic reserve of evolution. They make up 20-30% of the non-gene portion of DNA.

3. Mobile genetic elements:

TRANSPOSONS - sections of DNA that can be cut and inserted into other regions

DNA. These are the so-called "wanderers of genes".

RETROTRANSPOSONS - DNA segments that are copied within the genome, as inside

chromosomes and between them. They can change the meaning of human structural genes, lead to mutations. The human genome changes during life by 10 - 30%.

Damaged inactive, mobile genetic elements. They cannot be cut out or inserted due to the lack of REVERSE TRANSFERASE in the cell. If the fragment enters the cell with the virus, then these genes begin to be transcribed.

Main directions of molecular biology:

GENOMICS is a branch of molecular biology that studies the structure and mechanisms of the gene.

Transcriptomics is the study and identification of all mRNAs encoding proteins, the study of their number and patterns of expression of structural genes.

PH-omics is a branch of molecular biology concerned with the study and identification of all non-coding RNAs.

31. Mechanisms of DNA replication (matrix principle, semi-conservative method). Conditions required for replication. Stages of replication

Mechanisms REPLICATION - the process of DNA self-doubling. The replication mechanism is based on the principle of complementarity. The mechanism of replication is matrix biosynthesis. DNA replication proceeds in a semi-conservative way: a daughter chain is synthesized on each parent polynucleotide chain.

Conditions required for replication:

1. Matrix - DNA strands. The splitting of the strand is called REPLICATIVE FORK

2. Substrate. The plastic material is DEOXYNUCLEOTIDE TRIFOSPHATES:
dATP, dGTP, dCTP, dTTP.

3. Magnesium ions.

Replicative Enzyme Complex:

A) DNA unwinding proteins:

3. TOPOISOMERASES 1 and 2 (unwind over the helix). Break (3",5")-phosphodiester bonds.

C) DNA POLYMERASE (catalyses the formation of phosphodiester bonds). DNA POLYMERASE only lengthens an already existing strand, but cannot connect two free NUCLEOTS.

E) DNA LIGASE.

5. PRIMERS - "seed" for replication. This is a short fragment from ribonucleotide triphosphates (2 - 10)..

The main stages of replication.

I. INITIATION of replication.

Occurs under the influence of external stimuli (growth factors). Proteins bind to receptors on the plasma membrane and induce replication into the synthetic phase of the cell cycle. The meaning of initiation is to attach DNA-A to the replication point, which stimulates the divergence of the double helix. HELIKAZA also takes part in this. There are enzymes (TOPOISOMERASES) that cause unwinding over the helix. SSB proteins prevent the connection of daughter chains. A REPLICATIVE FORK is formed.

2. Formation of child threads.

This is preceded by the formation of PRIMERS with the help of PRIMASE. DNA polymerase acts and a daughter strand of DNA is formed. This process occurs according to the principle of complementarity, and the synthesis goes from the 5* to the 3* end of the synthesized thread.

A continuous chain will be built on one of the mother threads, and OKAZAKI fragments will be built on the opposite thread.

3. Removal of PRIMERS with EXONUCLASE,

4. Linking short fragments with DNA LIGASE.

Replicative complex (helicase, topoisomerase). Primers and their role in replication.

A) DNA unwinding proteins:

1. DNA-A (causes strand separation)

2. HELIKASES (cleave the DNA chain)

1. TOPOISOMERASES 1 and 2 (unwind over the helix). Break (3",5")-phosphodiester bonds.

B) Proteins that prevent the connection of DNA strands (SSB proteins)

C) DNA POLYMERASE (catalyses the formation of phosphodiester bonds). DNA-
POLYMERASE only lengthens the already existing thread, but cannot connect two free NUCLEOTIDES.

D) PRIMASE (catalyses the formation of a "seed" for synthesis).

E) DNA LIGASE.

5. PRIMERS - "seed" for replication. This is a short fragment consisting of RIBONUCLEOTIDE TRIFOSPHATES (2 - 10). The formation of PRIMERS is catalyzed by PRIMASE. There are enzymes (TOPOISOMERASES) that cause unwinding over the helix. SSB proteins prevent daughter chains from joining. A REPLICATIVE FORK is formed. Formation of child threads. This is preceded by the formation of PRIMERS by the PRIMASE enzyme. DNA polymerase acts and a daughter strand of DNA is formed. This process occurs in accordance with the principle of complementarity, and the synthesis proceeds from the 5" to the 3" end of the synthesized thread.

A continuous chain will be built on one of the parent strands, and a chain of short fragments (OKAZAKI fragments) will be built on the opposite strand. Removal of PRIMERS using EXONUCLASE.

32. RNA biosynthesis (transcription). transcription conditions.

Transcription is the transfer of information from DNA to RNA (RNA biosynthesis). Only certain parts of the DNA molecule undergo transcription. This part is called the TRANSCRIPTON. Eukaryotic DNA is discontinuous: sections carrying information (EXONS) alternate with areas that do not carry information (INTRONS). In DNA, from the 5 "end, a PROMOTOR region is isolated - the site of attachment of RNA POLYMERASE. From the 3" end - TERMINATOR zone. These areas are not transcribed. TRANSCRIPTION CONDITIONS.

1. Matrix - 1 strand of DNA. A transcriptional eye is formed.

2. Structural components - RIBONUCLEOSIDE-3-PHOSPHATES (ATP, GTP, CTP, UTP).

3. DNA-dependent RNA polymerase.

Transcription steps

MAIN STAGES OF TRANSCRIPTION.

1. INITIATION. It consists in the attachment of RNA POLYMERASE to the PROMOTER, which leads to the divergence of DNA strands. The impulse to attach the RNA polymerase is the attachment of the TBP protein to the TATA box.

2. ELONGATION (elongation). The connection of RIBONUCLEOSIDEMONONUCLEOTIDES and the formation of phosphodiester bonds between NUCLEOTIDES with the help of RNA POLYMERASE, which moves along the DNA strand. The addition of NUCLETIDES proceeds in accordance with the principle of complementarity, only there will be RIBONUCLEOTIDES and - UMF.

3. TERMINATION (end). It consists in the fact that many (up to 200 - 300) ADENYL NUCLEOTIDES - poly A are attached to the 3 "end of the formed RNA. An exact copy of the gene is formed. ADENYL NUCLEOTIDES protect the 3" end from the action of EXONUCLEASES. A protection is formed from the 5 "end, the so-called "CAP" (most often UDP). This resulting copy of the gene is called TRANSCRIPT.

4. PROCESSING (maturation).

2. 5-end capping

3. Formation of the polyadenyl sequence

4. SPLICING - removal of introns and connection of EXONS with each other. Plays an important role in the evolution of organisms

5. Alternative splicing - from one pre-mRNA, several IRNAs and, accordingly, several proteins are formed, which manifests itself in a variety of characters in organisms.

The main manifestations of the pathology of carbohydrate metabolism and possible causes of carbohydrate metabolism disorders at various stages of metabolism. (Write reactions). Glycemia as an indicator of the state of carbohydrate metabolism. Quantification of glycemia in normal and pathological conditions. Development diabetes.

Violation of carbohydrate metabolism can be at various stages. HYPO-, HYPERGLUCOSEMIA, GLUCOSURIA are indicators of carbohydrate iomen. GLUCOSURIA is possible if the value of the renal threshold is exceeded more than 10 mmol / l. Most often, violations of carbohydrate metabolism are possible at the following stages:

1. at the stage of intake of carbohydrates with food. A large load of carbohydrates leads to the development of HYPERGLUCOSEMIA, GLUCOSURIA, increased fat biosynthesis, and the development of obesity.

2. With damage to the mucous membranes of the gastrointestinal tract. When the gastric mucosa is damaged, the production of hydrochloric acid is disrupted. When the mucous membrane of the small intestine is damaged, the absorption and hydrolysis of food DISACCHARIDES is impaired.

When the pancreas is damaged, the digestion of glycogen, food starch under the influence of enzymes is disturbed. The most formidable disease is diabetes mellitus. In the pancreas, B-cells synthesize the protein insulin, which ensures the transport of glucose from the blood to the tissues. In case of insufficient production of insulin, HYPERGLUCOSEMIA, GLYCOSURIA, KETONURIIA develops. Energy hunger develops in the cells, which is compensated by the processes of GLUCONEOGENESIS and the intensification of the processes of oxidation of proteins and fats, which is accompanied by excessive production of ACETYL-KOA, NH3. NH3 is a toxic product, it creates the prerequisites for the condensation of ACETYL-KOA and the formation of ketone bodies:

With liver damage, the process of biosynthesis and breakdown of glycogen is disrupted. Hereditary diseases are observed in genetic defects of enzymes involved in the metabolism of carbohydrates. The most common are GLYCOGENOSIS (GIRKE, POMPE) and AGLYCOGENOSIS (LEWIS, ANDERSEN), which are associated with insufficient activity or complete absence of enzymes involved in the breakdown or synthesis of glycogen. In children, there is ALACTOSIA - lactose intolerance due to a genetic defect in ENTEROCYTE LACTASE.

Glucose in whole capillary blood on an empty stomach - 3.3 - 5.5 mmol / l

HYPERGLYCEMIA: Excess contrainsular hormones, insulin deficiency (IDDM), impaired receptor function (NIDDM), stress (adrenaline raises glucose levels), excess carbohydrate intake.

HYPOGLYCEMIA: insulin overdose, lack of contrainsular hormones in the body, starvation.

Ketone bodies (not more than 0.1 g / l) - acetone, acetoacetic acid, beta-hydroxybutyric acid. Dangerous in relation to KETOACIDOSIS. HYPOGLYCEMIA leads to convulsions and death. 0.1% of glycogen is renewed in brain tissue in 4 hours.

When carbohydrate metabolism is disturbed, brain function is impaired.

The main manifestations of the pathology of lipid metabolism and the possible causes of their occurrence at various stages of metabolism. Formation of ketone bodies in tissues. Ketoacidosis. The biological significance of ketone bodies.

1 .At the stage of intake of fats with food:

A. Abundant fatty food against the background of HYPODYNAMIA leads to the development of NUTRITIONAL OBESITY.

B. Insufficient intake of fats or their absence leads to HYPO- and AVITAMINOSIS A, D, E, K. DERMATITIS, vascular sclerosis may develop. The process of synthesis of PROSTAGLANDINS is also disrupted.

C. Inadequate dietary intake of LIPOTROPIC (choline, serine, inositol, vitamins B12, B6) substances leads to the development of fatty tissue infiltration.

2.At the stage of digestion.

A. When the liver and intestines are damaged, the formation and transport of blood lipoproteins is disrupted.

B. When the liver and biliary tract are damaged, the formation and excretion of bile acids involved in the digestion of food fats are disturbed. GSD develops. HYPERCHOLESTEROLEMIA is noted in the blood.

C. If the intestinal mucosa is affected and the production and supply of pancreatic enzymes are impaired, the fat content in the stool increases. If the fat content exceeds 50%, steatorrhea develops. The stool becomes colorless.

D. Most often in recent years among the population there is a lesion of beta-cells of the pancreas, which leads to the development of diabetes mellitus, which is accompanied by intense oxidation of proteins and fats in the cells. In the blood of such patients, HYPERKETONEMIA, HYPERCHOLESTEROLEMIA are noted. Ketone bodies and cholesterol are synthesized from ACETYL-KOA.

3. At the stage of cholesterol metabolism, the most common disease is ATHEROSCLEROSIS. The disease develops when the content of ATHEROGENIC FRACTIONS increases between tissue cells and blood LP and the content of HDL decreases, the purpose of which is to remove cholesterol from tissue cells to the liver for its subsequent oxidation. All drugs, with the exception of CHylomicrons, are rapidly metabolized. LDL lingers in the vascular wall. They contain a lot of TRIGLYCERIDES and CHOLESTEROL. They are phagocytosed and destroyed by LYSOSOME enzymes, with the exception of cholesterol. It accumulates in the cell in large quantities. Cholesterol is deposited in the intercellular space and encapsulated connective tissue. Atherosclerotic plaques form in the vessels.

LECTURE #25

Federal State Budgetary Educational Institution of Higher Education USMU of the Ministry of Health of Russia
Department of Biochemistry
Discipline: Biochemistry
LECTURE #25
Biochemistry of vitamins 1
Lecturer: Gavrilov I.V.
Faculty: medical and preventive,
Course: 2
Yekaterinburg, 2016

Plan:

1.
2.
3.
4.
5.
Definition of vitamins
Vitamin classifications
General Mechanisms of Vitamin Metabolism
General scheme of vitamin metabolism
Water-soluble vitamins - individual
representatives

vitamins
-
low molecular weight
organic
connections
varied
chemical nature, in whole or in part
indispensable to humans or animals,
involved in regulation and catalysis, and not
used in energy and plastic
purposes.

Vitamin-like substances
irreplaceable or partially irreplaceable
substances that can be used in
plastic purposes and as a source of energy
(choline, orotic acid, vitamin F, vitamin
U (methylmethionine), inositol, carnitine)

CLASSIFICATION OF VITAMINS

By physical properties:
1. Water soluble vitamins
Vitamin PP (nicotinic acid)
Vitamin B1 (thiamine);
Vitamin B2 (riboflavin);
Vitamin B5 (pantothenic acid);
Vitamin B6 (pyridoxine);
Vitamin B9, Sun (folic acid);
Vitamin B12 (cobalamin);
Vitamin H (biotin);
Vitamin C (ascorbic acid);
Vitamin P (bioflavonoids);

2. Fat soluble vitamins
Vitamin A (retinol);
Vitamin D (cholecalciferol);
Vitamin E (tocopherol);
Vitamin K (phylloquinone).
Vitamin F (a mixture of polyunsaturated
long-chain fatty acids arachidonic, etc.)

CLASSIFICATION OF VITAMINS

According to metabolic properties:
Enzymovitamins (coenzymes) (B1, B2, PP,
B6, B12, pantothenic acid, biotin,
folic acid);
Hormonovitamins (D2, D3, A);
Redox vitamins or antioxidant vitamins (C, E, A, lipoic acid);

Literally
designation
chemical name
physiological
Name
Vitamin A
retinol
antixerophthalmic
Vitamin B1
Vitamin B2
thiamine
riboflavin
antineuritic
Growth vitamin
Vitamin B3
pantothenic acid
antidermatitis
Vitamin B6
Vitamin Bc, B9
Vitamin B12
pyridoxine
follacin
cobalamin
antidermatitis
anti-anemic
anti-anemic
Vitamin C
Ascorbic acid
antiscorbutic
Vitamin PP
niacin
antipellargic
Vitamin H
biotin
Antiseborrheic
vitamin P
routine
permeability factor
vitamin D2
ergocalciferol
antirachitic
vitamin D3
1,25-yoxycholecalciferol
antirachitic
vitamin E
tocopherol
anti-sterile
vitamin K
naphthoquinones
antihemorrhagic

Metabolism of vitamins in the body (general provisions)

water soluble vitamins in the gut
absorbed by active transport
fat-soluble - in the composition of micelles.
water-soluble vitamins in the blood
transported freely or in
complex with proteins, fat-soluble
vitamins - in the composition of lipoproteins and in
complex with proteins.
Vitamins from the blood enter the cells
organs and tissues.

Water soluble in the liver and kidneys
vitamins are converted into coenzymes.
Some vitamins in the liver and skin
converted to active forms (D)
Active forms of vitamins realize their
biochemical and physiological effects.
Inactivated as xenobiotics and others
metabolic products.
From the body vitamins and their derivatives
excreted mainly in urine and feces.

Study plan (answer) of individual vitamins

1. content in food products(2-3 products
- no numbers)
2. chemical structure (base, reactive
capable factions)
3. role in metabolism (2-3 equations of chem.
reactions)
4. picture of hypo- and hypervitaminosis (2-3 symptoms,
arising from the mechanism of action)
5. daily requirement, preventive and
therapeutic dosage (a few mg or fractions
mg / day, = prophylactic dosage, x 10 =
therapeutic single (daily) dosage.

NICOTINIC ACID - VITAMIN PP

COOH
CONH 2
N
N
A nicotinic acid
Nicotinamide
Vitamin PP
Physicochemical characteristics. Let's badly dissolve in water, it is good - in alkalis.
daily requirement
for adults 15-25mg,
for children - 5-20 mg. From herbal products:
in fresh mushrooms - 6 mg%, in dried mushrooms up to 60 mg%.
in peanuts (10-16 mg%),
in cereals in buckwheat (4 mg%),
millet, barley (2 mg %),
oatmeal and pearl barley, as well as in rice (1.5 mg %)
In red beets - 1.6 mg%,
In potatoes (1-0.9 mg%), and in boiled 0.5 mg%.
in spinach, tomato, cabbage, swede, eggplant (0.50.7 mg%).

From animal products:
liver (15 mg%),
kidneys (12-15 mg%),
heart (6-8 mg%),
meat (5-8 mg%),
fish (3 mg%).
vitamin PP can be synthesized
from tryptophan (little).

Metabolism
FRPF FFn
ATP
FFn
ATP
ADP
Nicotinamide
nicotinamide mononucleotide
OVER+
NADP+
nicotinamide mononucleotide
NAD pyrophosphorylase NAD kinase
pyrophosphorylase

Role in metabolism

Pyridine dependent coenzyme (NAD,
NADP) CTK dehydrogenases, glycolysis,
PFP, etc.

Hypovitaminosis PP - pellagra

"THREE D"
1. Dermatitis - inflammation of the skin,
2. Diarrhea - loose stools,
3. Dementia - mental
backwardness.

Pellagra

VITAMIN B1 (THIAMIN)

Cl-
NH2
H2+
C N
N
H3C
CH 3
H2
CCH2OH
N
S
Vitamin B1 (thiamine)
Physicochemical characteristics. Water soluble, breaks down
heat treatment.
vitamin B non-toxic
The daily requirement of an adult is not less than 1.4-
2.4 mg.
The predominance of carbohydrates in food increases the need
organism in vitamin;
fats, on the contrary, dramatically reduce this need.
h
n
a0
I,
(3
8
2
-
9
4
%
-
n
A
I
Thiamine content in mg% (mg/100g)
X
l
e
b
And
h
c
e
Dry brewer's yeast 5.0, baker's yeast 2.0
Wheat (germs) 2.0
Ham 0.7
Soya 0.6
Buckwheat 0.5
Barley (grain) 0.4
Wheat (whole grain) 0.4
Pork liver, cattle 0.4

Oats (grain) 0.4
Oatmeal 0.3
Wheat flour (82-94%) 0.3
Barley groats 0.2
Whole rye flour 0.2
Meat (other) 0.2
Rye bread 0.15
Corn (whole grain) 0.15
Cow's milk 0.05
Wheat bread from fine flour 0.03

Metabolism
1. Absorption: in the intestine;
2. Transport: in free form;
3. Activation: with the participation of thiamine kinase and ATP in
liver, kidney, brain and heart muscle vitamin
B1 is converted into an active form - a coenzyme
thiamine pyrophosphate (TDF, TPP)
NH2
NH2
N
H3C
H2+
C N
ATP
CH 3
H2
CCH2OH
N
S
Vitamin B1 (thiamine)
AMF
H3C
Thiaminkinase
H2+
C N
N
N
S
CH 3
O
O
H2 H2
C C O P O P OH
O
O
Thiamine diphosphate (TDP)

Biological role
TPP is included in:
pyruvate dehydrogenase complex
(PVK → Acetyl-CoA);
α-ketoglutarate dehydrogen complex
(α-KG → Succinyl-CoA);
transketolase PFS
(transfer of aldehyde from ketosaccharide to aldosaccharide)

Mechanism
TDF takes the group from the substrate and transfers it to lipoic acid
NH2
H2
C N
N
COOH
CO
H3C
N
S
CH 3
O
O
H2 H2
C C O P O P
O
O
Oh
S
Thiamine pyrophosphate (TDP)
CH 3
NH2
CO2
N
H3C
PYRUVATE DEHYDROGENASE
H2
C N
N
S
CH 3
O
O
H2 H2
C C O P O P
O
O
Lipoic acid
SH
HSKoA
CO
CH 3
Lipoic acid
SKoA
Oh
S
S
ABOUT
COH
CH 3
Hydroxyethyl-TDF
CH3

Hypovitaminosis B1 (Take - Take)

It proceeds with a predominance of one of the forms:
1. dry (disorders of the nervous system). polyneuritis, in
basis - degenerative changes in the nerves. At the beginning
pain develops along the nerve trunks, then
- loss of skin sensation and paralysis occurs
(Beri-Beri disease). There is memory loss
hallucinations.
2. edematous (violations of cardio-vascular system),
manifested as arrhythmias, increased
the size of the heart and the appearance of pain in the region of the heart.
3. cardiac (acute heart failure,
myocardial infarction).
Signs also include violations of the secretory and motor
functions of the gastrointestinal tract; decrease in gastric acidity,
appetite, intestinal atony. Develops negative nitrogen
balance.

take take

VITAMIN B2 (RIBOFLAVIN)
O
H3C
H3C
N
NH
O
N
isoalloxazine
N
H H H
H2C C C C CH2OH
OH OH OH
ribitol
Vitamin B2 (riboflavin)
Physicochemical characteristics. crystals yellow color, slightly soluble
in water.
Physiological daily requirement in an adult
human 2-2.5 mg / day.
in newborns - 0.4-0.6 mg,
in children and adolescents - 0.8-2 mg.

The content of vitamin B2 in food
products mg % (mg/100 g mass)
1. Liver (beef) 1.5
2. Chicken egg 0.6
3. Wheat 0.3
4. Milk 0.2
4. Cabbage 0.2
6. Carrot 0.05
Breaks down in the presence of ultraviolet light
rays. When storing milk in the light for three and a half
hours, up to 70% of the vitamin is destroyed.
when heated, it is destroyed in an alkaline environment,
but in an acidic environment, resistant to high
temperature (290°C).

Metabolism
Absorption: in the intestine;
Transport: in free form;
Activation:
V
mucous
shell
intestines
going on
education
coenzymes FMN and FAD:
ATP
ADP
ATP
FFn
Riboflavin
FAD
FMN
Riboflavin kinase FMN-adenylyl transferase

Role in metabolism
The coenzymes FAD and FMN are part of the aerobic and
anaerobic dehydrogenases involved in
redox reactions (reactions
oxidative phosphorylation, SDH, AA oxidase,
xanthion oxidase, aldehyde oxidase, etc.).
O
H3C
H3C
N
Succinate Fumarate
H3C
NH
O
N
N
H H H
H2C C C C CH 2OPO 3H2
OH OH OH
FMN
SDG
H3C
H
N
O
NH
O
N
N
H
H H H
H2C C C C CH 2OPO 3H
OH OH OH
FMNN2

HYPOVITAMINOSIS B2

Stopping body growth
Inflammation of the oral mucosa
cavities (glossitis - inflammation of the tongue), appear
long-term non-healing cracks in the corners of the mouth,
nasolabial fold dermatitis.
Inflammation of the eyes in the form of vascularization of the cornea
membranes, keratitis, cataracts.
Skin lesions(dermatitis, alopecia,
peeling of the skin, erosion, etc.).
general muscle and heart weakness
muscles.

PANTOTHENIC ACID (VITAMIN B5)
CH3OH
HOH 2C
C
CH
CH 3
C
H
N
H2 H2
C C
COOH
O
Vitamin B5
white fine crystalline powder, soluble in water.
Sources. Synthesized by plants and microorganisms
found in many animal and vegetable products
origin (egg, liver, meat, fish, milk, yeast,
potatoes, carrots, wheat, apples). In the human intestine, pantothenic acid is produced in small amounts by the intestinal
wand.

Absorption: in the intestine;
Transport: in free form;
Activation: from pantothenic acid in cells
coenzymes are synthesized: 4-phosphopantotheine and
HSCoA.
CH3OH
H H2 H2
HOH 2C C CH C N C C COOH
CH 3
O
Pantothenic acid
ATP
ADP
pantotheine kinase
CH3OH
H2
H H2 H2
H2O3PO C C CH C N C C COOH
CH 3
O
4-phosphopanthotheine

Role in metabolism
4-phosphopanthotheine - coenzyme
palmitoyl synthase.
HS-CoA
involved
c: radicals in reactions
1. transfer
acyl
common pathway of catabolism,
2. activation of fatty acids,
3. synthesis of cholesterol and ketone bodies,
4. synthesis of acetylglucosamines,
5. neutralization of foreign substances in the liver

HYPOVITAMINOSIS B 3

Dermatitis, mucosal lesions,
dystrophic changes.
Damage to the nervous system
(neuritis, paralysis).
Changes in the heart and kidneys.
Hair depigmentation.
Cessation of growth.
Loss of appetite and emaciation.

VITAMIN B6 (PYRIDOXINE,
PYRIDOXAL, PYRIDOXAMINE)
Distribution: Liver, kidneys,
meat, bread, peas, beans,
potato.
Absorption: in the intestine
Transport: in free form;
Activation:
by the action of pyridoxalkinase
converted to coenzymes
pyridoxal phosphate and
pyridoxamine phosphate.1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Oats 3.3
Wheat 3.3
Baker's yeast 2.0
Cow's milk 1.5
Mackerel 1.03
Liver 0.64
Nuts (hazelnuts) 0.59
Carrot 0.53
Soybeans 0.38
Potato 0.33
Bananas 0.29
Chicken egg 0.12

daily requirement

adult - 3 - 4 mg,
newborn
- 0.3 - 0.5 mg,
children and adolescents - 0.6 - 1.5 mg.

CHO
HO
H3C
CHO
CH2OH
ATP
ADP
pyridoxalkinase
N
Pyridoxal
Vitamin B6
HO
H3C
H2
C O PO 3H2
N
Pyridoxal phosphate
coenzyme

Role in metabolism
(amino acid exchange, transfer of amino groups)
Pyridoxal enzymes play a key role
role in AK exchange:
1. catalyze transamination reactions and
decarboxylation of amino acids,
2. participate in specific reactions
metabolism of individual AAs: serine,
threonine, tryptophan, sulfur-containing
amino acids,
3. in heme synthesis.

B6-coenzyme

1.
2.
3.
4.
5.
amino acid isomerase. Utilization in the body
D-amino acids
Amino acid decarboxylases. Education
biogenic amines
Monoamine oxidase. Diaminooxidase
(histaminases). Oxidation (inactivation) of biogenic
amines
Aminotransferase amino acids. catabolism and
amino acid synthesis
Aminotransferases of iodotyrosines and iodothyronines.
Biosynthesis of iodothyronines (hormones) in the thyroid
iron and their catabolism. Aminotransferase γaminobutyrate. Neutralization of GABA
glycogen phosphorylase. Glycogenolysis

Hypovitaminosis B6

Dermatitis, mucosal lesions
Homocystinuria
Tryptophan metabolism disorders
convulsions

BIOTIN (VITAMIN H)
Content in food
shark liver pork and beef
liver, kidneys and heart of a bull, egg
yolk, beans, rice bran,
wheat flour cauliflower.

Role in metabolism
performs a coenzyme function in the composition of carboxylase:
formation of the active form of CO2:
O
O
CO2 + ATP
HN
ADP + Fn
NH
HN
N
H2 H2 H2 H2
C C C C COOH
S
CO2 activation
COOH
H2 H2 H2 H2
C C C C COOH
S

Role in metabolism

1.used in the formation of malonyl-CoA from acetyl-CoA;
2.in the synthesis of the purine ring;
3.in PVC carboxylation
4.in the synthesis of fatty acids, proteins and
purine nucleotides.

Hypovitaminosis vit. H

dermatitis
secretions of the sebaceous glands
hair loss
nail lesions
muscle pain
fatigue
drowsiness
depression
anemia

Folic acid

Oh
N
N
H2N
N
O
H2
C
H
N
C
H
C
H2
C
H2
C
COOH
COOH
N
2-amino-4-hydroxy-6-methylpterin
H
N
PABC
Glutamate
Vitamin: folic acid (folate, vitamin B9, vitamin Bc, vitamin M)
Pale yellow hygroscopic crystals,
decomposing at 250 °C, slightly soluble
in water (0.001%).

Norm: 200-400 mcg / day (pregnant women 800 mcg / day)
Synthesize folic acid
microorganisms, lower and higher plants
Sources folic acid
1. food (a lot in green vegetables with
leaves, in some
citrus fruits, in legumes, in bread
from wholemeal flour,
yeast, liver).
2. intestinal microflora (bad).
Fresh leafy vegetables stored at room temperature may
lose up to 70% folate in 3 days
During cooking, up to 95% of folate is destroyed.

Activation, metabolism and excretion of folic acid

gastrointestinal tract
Binding
Folic acid + Castle factor
Folic acid + blood proteins
Suction: 12 duodenum
Oh
Liver
O
N
N
H2N
Blood
5 - 20 mcg/liter
N
H2
C
H
N
C
H
N
H
C
H2
C
H2
C
COOH
COOH
N
2-amino-4-hydroxy-6-methylpterin
2NADPH2
PABC
Glutamate
Folic acid
Dehydrofolate reductase
2NADP+
Oh
2/3 in the liver
N
N
H2N
H
N
N
H
H H
2
C C
CH
O
H
N
H
C
H
N
H
C
H2
C
H2
C
COOH
COOH
Tetrahydrofolic acid (THFA)
1% of the total supply / day
Urine
1/3 in fabric

Role of THFC

Participates:
in amino acid metabolism
(serine
glycine, homocysteine
methionine),
in the synthesis of nucleic acids (purine
bases, thymidylic acid),
in the formation of red blood cells
in the formation of a number of components of the nervous
tissuefolic acid
reduces the level of homocysteine ​​in the blood

1. one-carbon fragments are attached to THPA
2. in THPA, one-carbon fragments interconvert
3. One-carbon fragments of THPA are used for the synthesis of:
H
Methionine
Homocysteine
Methionine synthase
3
TMF
DUMF
H
Ser
H
R1N
5
N R2
10
H2
C
gli
R1N
5
1
Purines
NADH2 NAD+
N R2
10
CH 3
R1N
5
2
H
N R2
10
N5-methyl-THPA
N5N10-methylene-THPA
THFC
+
NADP
5,10-methyleneTHFA reductase
Serinoxymethyltransferase
2
HN
CH
R1N
5
NH3
H
N R2
10
N5-formimino-THPA
2
H
C
R1N
5
Purines
NADPH2
H2O
N R2
10
N5N10-methylenyl-THPA
H+
2
HOHC
R1N
5
N R2
10
N10-formyl-THPA

The role of THPA in DNA synthesis
DNA
Purines

Folic acid hypovitaminosis
Folic acid deficiency leads to:
Megaloblastic anemia
Neural tube defects in the fetus.

The development of hyperhomocysteinemia
1. Homocysteine ​​has a pronounced toxic
action on the cell: leads to damage and
activation of endothelial cells
lining of blood vessels), which contributes to
development of thrombosis, atherosclerosis.
2. Hyperhomocysteinemia is associated with such
obstetric pathology:
early pregnancy loss,
early onset of gestosis,
placental abruption,
intrauterine growth retardation.

To methionine deficiency
Methionine deficiency is accompanied
serious metabolic disorders
primarily lipid metabolism, and
causes severe injury
liver, in particular its fatty
infiltration.

VITAMIN B12 (COBALAMIN)
Absorption: Intrinsic Factor Castle - protein -
gastromucoprotein, synthesized by parietal
stomach cells. In the gastrointestinal tract, the Castle factor
combines with vitamin B12 with the participation of Ca2 +,
protects it from destruction and provides
absorption in the small intestine.
Transport: B12 enters the blood in combination with
proteins transcobalamins I and II,
(I) acts as a B12 depot because
He
most strongly associated with the vitamin.
Activation. Vitamin B12 produces 2
coenzyme: methylcobalamin in the cytoplasm and
deoxyadenosylcobalamin in mitochondria.

daily requirement

adults 2 - 4 mcg,
in newborns - 0.3-0.5 mcg,
in children and adolescents - 1.5-3.0 mcg.
Content in food products in µg%
1 Pork liver 26
2 Pork kidneys 15
3 Fish 2.0
4 Lamb 2
5 Chicken egg 1.1
6 Pork 2
7 Beef 2
8 Mackerel 6
9 Cheese 1.1
10 Whole milk 0.4

Role in metabolism

coenzyme of metabolic reactions
transfer of alkyl groups (-CH2-, -CH3);
homocysteine ​​methylation
Methylcobalamin is involved: in education
methionine from homocysteine ​​and
transformations of one-carbon fragments into
composition of THPA required for the synthesis
nucleotides.
Deoxyadenosylcobalamin is involved in:
metabolism of fatty acids with an odd number
carbon atoms and AA with branched
hydrocarbon chain.

Participation of vitamin B12 in metabolism
the sequence of the conversion of vitamin B12 into a coenzyme:
cyanocobalamin oxycobalamin deoxyadenosylcobalamin
1. Exchange of H for -COOH, -NH2, -OH groups
2. Recovery of ribonucleotides in
deoxyribonucleotides
3. Transmethylation reactions

AT 12
Folic acid ------ THFA ------
nucleic acid synthesis

Avitaminosis and hypovitaminosis
Endogenous
Gastrogenic
Exogenous
Enterogenic
Manifestations: malignant macrocytic,
megaloblastic anemia;
CNS disorders (funicular
myelosis);
gastric pH
(gastroenterocolitis -
"polished tongue")

The first mention of the disease (kakke, beriberi), now known as a manifestation of thiamine deficiency, are found in ancient medical treatises that have come down to us from China, India, and Japan. By the end of the 19th century, several forms of this pathology were already clinically distinguished, but only Takaki (1887) associated the disease with what he then believed to be a lack of nitrogen-containing substances in the diet. The Dutch doctor S. Eijkman (1893-1896) had a more definite idea, who discovered then unknown factors in rice bran and in some leguminous plants that prevented the development or cured beriberi. Purification of these substances was then carried out by Funk (1924), who first proposed the term "vitamin" itself, and a number of other researchers. The active substance extracted from natural sources was characterized only in 1932 by a general empirical formula, and then in 1936 it was successfully synthesized by Williams et al. As early as 1932, the role of the vitamin in one of the specific metabolic processes, the decarboxylation of pyruvic acid, was suggested, but only in 1937 did the coenzyme form of the vitamin, thiamine diphosphate (TDP), become known. The coenzymatic functions of TDP in the system of decarboxylation of alpha-keto acids have long been considered almost the only biochemical mechanisms for the implementation of the biological activity of the vitamin, however, already in 1953, the range of enzymes that depend on the presence of TDP was expanded due to transketolase, and relatively recently, the specific gamma-hydroxy decarboxylase -alpha-ketoglutaric acid. There is no reason to think that the prospect of further study of the vitamin is exhausted by the above, since animal experiments, data obtained in the clinic during the therapeutic use of the vitamin, analysis of the facts illustrating the known neuro- and cardiotropism of thiamine, undoubtedly indicate the presence of some more specific connections. vitamin with other biochemical and physiological mechanisms.

Chemical and physical properties of vitamin B1

Thiamine or 4-methyl-5-beta-hydroxyethyl-N-(2-methyl-4-amino-5-methylpyrimidyl)-thiazolium, is obtained synthetically, usually in the form of a hydrochloride or hydrobromide salt.

Thiamine chloride (M-337.27) crystallizes in water in the form of colorless monoclinic needles, melts at 233-234° (with decomposition). In a neutral medium, its absorption spectrum has two maxima - 235 and 267 nm, and at pH 6.5 one - 245-247 nm. The vitamin is highly soluble in water and acetic acid, somewhat worse in ethyl and methyl alcohols, and insoluble in chloroform, ether, benzene, and acetone. From aqueous solutions, thiamine can be precipitated with phosphotungstic or picric acid. In an alkaline environment, thiamine undergoes numerous transformations, which, depending on the nature of the added oxidizing agent, may result in the formation of thiamine disulfide or thiochrome.

In an acidic environment, the vitamin decomposes only with prolonged heating, forming 5-hydroxy-methylpyrimidine, formic acid, 5-aminomethylpyrimidine, the thiazole component of the vitamin and 3-acetyl-3-mercapto-1-propanol. Among the decomposition products of the vitamin in an alkaline medium, thiothiamin, hydrogen sulfide, pyrimidodiazepine, etc. were identified. Sulfate and vitamin mononitrate were also obtained. Thiamine salts with naphthalenesulfonic, arylsulfonic, cetylsulfuric and esters with acetic, propionic, butyric, benzoic and other acids are known.

Of particular importance are thiamine esters with phosphoric acid, in particular TDP, which is the coenzyme form of the vitamin. Homologs of thiamine were also obtained by various substitutions at the second (ethyl-, butyl-, hydroxymethyl-, hydroxyethyl-, phenyl-, hydroxyphenyl-, benzyl-, thioalkyl-), fourth (oxythiamine) and sixth (methyl-, ethyl) carbon atoms of pyrimidine methylation of the amino group, substitution of the thiazole ring for pyridine (pyrithiamine), imidazole or oxazole, modifications of substituents at the fifth carbon of thiazole (methyl-, hydroxymethyl-, ethyl, chloroethyl-, hydroxypropyl-, etc.). A separate large group of vitamin compounds are S-alkyl and disulfide derivatives. Among the latter, thiamine propyl disulfide (TPDS) has received the greatest distribution as a vitamin preparation.

Methods for determining vitamin B1

In pure aqueous solutions, the quantification of thiamine is most easily carried out by absorbance at 273 nm, which corresponds to the isosbestic point of the spectrum of the vitamin, although some authors prefer to work in the 245 nm region, in which extinction changes are most noticeable. At pH 7.3 in phosphate buffer, thiamine, even at a concentration of 1 μg/ml, gives a distinct hydrogen polarographic catalytic wave, and in an alkaline medium it forms an anode wave due to the interaction of thiolthiamine with mercury and the formation of mercaptide. Both polarographic characteristics can be used to quantify the vitamin. If it is necessary to investigate various vitamin derivatives, then one has to resort to their preliminary separation by electrophoresis or chromatography.

The most successful general principle for the colorimetric determination of a vitamin is its reaction with various diazo compounds, among which diazotized p-aminoacetophenone gives the best results. The resulting brightly colored compound is easily extracted from the aqueous phase into an organic solvent, in which it is easily subjected to quantitative photometry. In phosphate buffer pH 6.8, thiamine, when heated, also interacts with ninhydrin, giving a yellow color proportional to the vitamin concentration in the range of 20-200 μg.

The most widespread are various variants of the fluorimetric determination of vitamin, based on the oxidation of thiamine to thiochrome in an alkaline medium. Preliminary purification of the test material from impurities that interfere with subsequent fluorometry is achieved by short-term boiling of samples with dilute mineral acids, removal of impurities by extraction with butyl or amyl alcohols, or isolation of the vitamin on appropriate adsorbents. As studies by Japanese authors have shown, instead of potassium ferricyanide, it is preferable to use cyanogen bromide as an oxidizing agent, which gives a higher yield of thiochrome and reduces the formation of other compounds that interfere with the determination. For a satisfactory determination of thiamine, 100-200 mg of tissue or 5-10 ml of blood is required. Considering that the main form of the vitamin present in tissues is TDP or proteinized disulfide derivatives of thiamine, pretreatment of the test samples (weak acid hydrolysis, phosphatase, reducing agents) is always necessary to release free thiamine, since other forms of the vitamin do not form thiochrome, extractable then for fluorimetry in an organic solvent.

Quantitative determination of the coenzyme form of the vitamin is carried out by recombination of TDP contained in the test solution with friendly apocarboxylase. In both cases, in the presence of magnesium and pyruvate ions, specific decarboxylation of ketoacid occurs, and the amount of carbon dioxide released (in the Warburg apparatus) is proportional to the amount of TDP added to the sample (0.02-1 μg). The sensitivity (0.005-0.06 µg TDP) of the method based on the enzymatic determination of acetaldehyde formed in the first reaction is even higher. The addition of alcohol dehydrogenase along with apocarboxylase and a specific substrate to the incubation medium makes it possible to very quickly (5-7 minutes) record the reaction by changing the extinction of the solution at 340 nm in the region corresponding to NADH2.

Other thiamine phosphates are determined quantitatively after their electrophoretic or chromatographic separation, subsequent elution, dephosphorylation with phosphatases and fluorimetry of thiochrome obtained by oxidation in an alkaline medium. Microbiological methods for the determination of thiamine are based on the selection of appropriate cultures of microorganisms sensitive to vitamin deficiency. The most accurate and reproducible results are obtained by using Lactobacillus fermenti-36 for these purposes.

Distribution of vitamin B1 in nature

Product	Thiamine content in µg%	Product	Thiamine content in µg%
Wheat	0,45	tomatoes	0,06
Rye	0,41	Beef	0,10
Peas	0,72	Mutton	0,17
Beans	0,54	Pork	0,25
oatmeal	0,50	Veal	0,23
Buckwheat	0,51	Ham	0,96
Semolina	0,10	chickens	0,15
Rice polished	0	chicken eggs	0,16
Pasta	footprints	Fresh fish	0,08
Wheat flour	0,2-0,45	cow's milk	0,05
Rye flour	0,33	Fruits are different	0,02-0,08
wheat bread	0,10-0,20	Dried brewer's yeast	5,0
Rye bread	0,17	walnuts	0,48
Potato	0,09	groundnuts	0,84
white cabbage	0,08

Thiamine is ubiquitous and found in various representatives of wildlife. As a rule, its amount in plants and microorganisms reaches values ​​much higher than in animals. In addition, in the first case, the vitamin is presented mainly in the free form, and in the second - in the phosphorylated form. The content of thiamine in basic foodstuffs varies over a fairly wide range depending on the place and method of obtaining raw materials, the nature of the technological processing of semi-finished products, etc. which in itself significantly destroys thiamine. On average, it can be considered that conventional cooking destroys about 30% of the vitamin. Some types of processing (high temperature, high pressure and the presence of large amounts of glucose) destroy up to 70-90% of the vitamin, and preservation of products by treating them with sulfite can completely inactivate the vitamin. In cereals and seeds of other plants, thiamine, like most water-soluble vitamins, is contained in the shell and germ. Processing of vegetable raw materials (removal of bran) is always accompanied by a sharp decrease in the level of the vitamin in the resulting product. Polished rice, for example, does not contain the vitamin at all.

Thiamine metabolism in the body

Vitamin comes with food in free, esterified and partially bound form. Under the influence of digestive enzymes, it is almost quantitatively converted into free thiamine, which is absorbed from the small intestine. A significant part of the thiamine that enters the bloodstream is rapidly phosphorylated in the liver, part of it in the form of free thiamine enters the general circulation and is distributed to other tissues, and part is again released into the gastrointestinal tract along with bile and excretions of the digestive glands, providing constant recycling of the vitamin and gradual , uniform assimilation by its tissues. The kidneys actively excrete the vitamin into the urine. In an adult, from 100 to 600 mcg of thiamine is secreted per day. The introduction of increased amounts of vitamin with food or parenterally increases the excretion of the vitamin in the urine, but as the dose increases, the proportionality gradually disappears. In the urine, along with thiamine, the products of its decay begin to appear in increasing quantities, which, with the introduction of the vitamin over 10 mg per person, can be up to 40-50% of the original dose. Experiments with labeled thiamine showed that, along with unchanged vitamin, a certain amount of thiochrome, TDS, pyrimidine, thialose components and various carbon- and sulfur-containing fragments, including labeled sulfates, are found in the urine.

Thus, the destruction of thiamine in the tissues of animals and humans occurs quite intensively, but attempts to detect enzymes in animal tissues that specifically destroy thiamine have not yet yielded convincing results.

The total content of thiamine in the entire human body, normally provided with vitamin, is approximately 30 mg, and in whole blood it is 3-16 μg%, and in other tissues it is much higher: in the heart - 360, liver - 220, in the brain - 160, lungs - 150, kidneys - 280, muscles - 120, adrenal gland - 160, stomach - 56, small intestine - 55, large intestine - 100, ovary - 61, testicles - 80, skin - 52 mcg%. In the blood plasma, predominantly free thiamine (0.1 - 0.6 μg%) is found, and in erythrocytes (2.1 μg per 1011 cells) and leukocytes (340 μg per 1011 cells) - phosphorylated. Almost half of the vitamin is in the muscles, 40% in the internal organs, and 15-20% in the liver. The main amount of tissue thiamine is represented by TDP, although the skin and skeletal muscles contain quite a lot of vitamin disulfides.

Normally, free thiamine is easily determined in the intestines and kidneys, which may also be due to shortcomings of a purely methodological order, since these tissues have an exceptionally high phosphatase activity, and by the time the material is taken for research, partial dephosphorylation of vitamin esters can already occur. On the other hand, these same mechanisms may play a role in removing the vitamin from the blood into urine or feces. The amount of vitamin in human feces is approximately 0.4-1 μg and practically does not depend on the biosynthesis of the vitamin by the intestinal microflora.

Some idea of ​​the dynamics of the exchange of tissue reserves of the vitamin is given by experiments carried out with S35-thiamine. Thiamine renewal occurs in different tissues at different rates and practically complete replacement non-radioactive vitamin to radioactive (introduced daily) is carried out by the 8th day of the experiment only in the liver, kidneys, spleen and skeletal muscles. In the heart, pancreas and brain tissue, this process does not end by the specified time. These data show that the amount of vitamin found in tissues is many times higher than the level required to provide specific TDP enzyme systems. Apparently, significant amounts of the vitamin are present in tissues, especially in the heart and liver, in the form of its derivatives that perform some other non-coenzymatic functions.

Mechanisms of deposition of thiamine in the body

The fixation of the vitamin in tissues is mainly associated with the formation of TDP, which makes up at least 80-90% of all thiamine found in the body. Some uncertainty on this issue is associated with the detection along with TDP, especially in short intervals after the administration of the vitamin, other TFs and mixed thiamine disulfides. Under certain conditions, from 10 to 30% of the vitamin may be represented by TMF and TTP. In addition, TTP is easily converted to TDP during the processing of biological material before the study. Like other phosphorylated coenzymes, TDP is fixed on proteins by its pyrophosphate moiety. However, other parts of the vitamin molecule play an equally active role in this.

Formation of thiamine phosphates (tf)

The reaction of phosphorylation of thiamine occurs due to ATP according to the general equation: thiamine + ATP-> TDP + AMP.

The regularities of this reaction were confirmed on a partially purified preparation of thiamine kinase from a soluble fraction of the liver homogenate. The optimum pH for the formation of TDP by this enzyme preparation was in the range of 6.8-6.9. Phosphorylation of thiamine was inhibited by AMP and ADP. In the presence of AMP, only traces were formed, and in the presence of ADP, very small amounts of TDP were formed. If TMF was introduced into the medium instead of thiamine, the formation of TDP was inhibited. A thiamykinase preparation purified approximately 600 times was used to study the mechanism of vitamin phosphorylation using labeled gamma-P32-ATP. It turned out that thiamine receives the entire pyrophosphate group from ATP.

In a series of works on the study of thiamine kinase isolated from yeast and animal tissues, it was found that manganese, magnesium and cobalt ions activated, while calcium, nickel, rubidium and iron did not inhibit the enzyme in a wide range of concentrations. The same works show the possibility of phosphorylation of thiamine at the expense of other nucleotide triphosphates (GTP, ITP, UTP, etc.) and that the main reaction product is TDP and a small amount of TMP. The use of P32-ATP, as in the studies of previous authors, confirmed the mechanism of direct transfer of the pyrophosphate group to thiamine.

However, the results obtained in vitro have not been fully confirmed in the study of thiamine phosphorylation in the body and in experiments with mitochondria. On the one hand, after intravenous administration of thiamine, phosphorus-labeled TDP and TTP, but not TMF, were found in the blood of animals after 30-60 minutes; the mechanism of pyrophorylation was confirmed. On the other hand, after the intravenous administration of TMF, the cocarboxylase and transketolase activity of the blood increased faster than after the administration of free thiamine. Some microorganisms form TDP more easily from TMF than from the free vitamin, and thiamine kinase, previously found in the liver, is not found in kidney mitochondria, in which thiamine phosphorylation proceeds in a different way. The mechanism of vitamin phosphorylation involving only ATP does not always fit into a simple scheme of transfer of the pyrophosphate group as a whole, if only because, along with TDP, other TFs, including even T-polyphosphates, are found in significant amounts in various biological material.

A number of studies dealt with the question of the localization of the systems responsible for thiamine phosphorylation. An hour after the administration of thiamine, the liver captures 33-40% of the vitamin, accumulating its various phosphoric esters. Phosphorylation of the labeled vitamin in different organs occurs in descending order of activity: liver, kidneys, heart, testes, brain. In this case, the radioactivity of phosphoric esters of thiamine decreases in the series: TTP, TDP, TMF. Phosphorylation of thiamine is active in mitochondria, microsomes and hyaloplasm.

From the above facts, it is not difficult to conclude that the overall intensity of vitamin esterification processes in the body or in individual tissues should largely correlate with the activity of the processes that supply ATP. The first experimental observations in this regard, carried out on liver homogenates or blood cell elements, were subsequently fully confirmed. All inhibitors of respiration and glycolysis, or compounds that compete with T for ATP, tend to reduce the level of TDP in the blood and tissues.

The role of individual groups in the thiamine molecule for its binding in tissues

To date, a large number of new thiamine derivatives (mixed disulfides, O-benzoyl derivatives, etc.) have been synthesized and are widely introduced into medical and preventive practice. The advantages of new vitamin preparations, as a rule, were revealed purely empirically due to the fact that so far we do not have sufficient information about the molecular mechanisms of thiamine assimilation, about the nature of its interaction with specific (enzymes) and nonspecific (transporting vitamin) proteins. The need for accurate representations in this matter is also dictated by the broad prospects for the use of thiamine antivitamins (amprol, chlorothiamine, deoxythiamine) for therapeutic purposes (see below).

Work on the synthesis of new thiamine derivatives with predetermined physicochemical properties, which determine the possibility of a targeted impact on metabolic processes in the body, is unthinkable without specific ideas about the role of individual groups of vitamins atoms and its derivatives in this area. The significance of the pyrophosphate radical for the specific proteidization of TDP in the composition of the corresponding enzymes has already been noted above. A large amount of data has appeared proving the participation of thiamine in other reactions that have nothing to do with the coenzyme functions of the vitamin. It can be assumed that the variety of active groups in the thiamine molecule corresponds to special forms of pretheidization, in which some are blocked and other, important for the corresponding function, sections of the vitamin molecule are opened simultaneously. Indeed, the first type of proteinization (through the pyrophosphate radical) corresponds to the coenzyme function and leaves the 2nd carbon of the thiazole and the amino group of the pyrimidine component free, accessible to the substrate. On the other hand, it is obvious that the participation of the vitamin in redox reactions or in the processes of rephosphorylation should be combined with the exclusion of the possibility of its simultaneous functioning as a coenzyme, since in the first case depolarization and opening of the thiazole ring is necessary, and in the second - the free position of the phosphorylated hydroxyethyl radical . Since 80-90% of the thiamine present in tissues is released only during acidic and enzymatic hydrolysis, it can be assumed that all bound forms of the vitamin are in a proteidized, i.e., associated with proteins, state.

It is easy to get an idea of ​​the significance of individual sections of the thiamine molecule in this process by determining the degree of binding by tissues of the sulfur-labeled (S35) vitamin and some of its derivatives, devoid of certain active centers, for example, the amino group - oxythiamine (oxy-T), the amino group and the hydroxyethyl radical - chloroxythiamine (XOT), quaternary nitrogen in the thiazole cycle - tetrahydrothiamine (TT). Without touching on the details of the question raised, it can be stated with sufficient confidence that structural modifications of at least one site in the vitamin molecule drastically violate (see table) the conditions for its_binding by tissues: after 24 hours, all introduced labeled thiamine derivatives bind worse than vitamin.

By itself, this fact indicates that not one or two, but, apparently, several groups play a role in the interaction of thiamine with proteins.

Coenzyme functions of thiamine diphosphate

A significant number of different reactions catalyzed by TDP are known. However, all of them can be reduced to several typical options: simple and oxidative decarboxylation of alpha-keto acids, acyloin condensation, phosphoroclastic cleavage of ketosaccharides. Enzyme systems taking part in these reactions, apparently, are united in the basic principles of their action; only the subsequent fate of the "active aldehyde fragment" that appears at the first stages of the process is different. Studies of the transformations of alpha-keto acids made it possible to clearly understand both the role of the decarboxylating fragment of the polyenzymatic complex of dehydrogenase containing TDP and the sequence of all other reactions associated with it.

In the transketolase (TK) system, the “active aldehyde” fragment will obviously be represented by a glycol radical transferred from the corresponding sources (xylulose-5-phosphate, fructose-6-phosphate, hydroxypyruvate, etc.) to various acceptors (ribose-5-phosphate , erythrose-4-phoophate, glucose-6-phosphate). In the phosphoketolase reaction, the "active glycol" radical is converted directly to acetyl phosphate.

Significant progress in elucidating the mechanism of the catalytic action of TDP was achieved as a result of studies carried out in two main directions: the creation of model non-enzymatic systems and the introduction of various thiamine analogues or antagonists into enzymatic systems. Using the first way, it was possible to show that vitamin B1, even in its non-phosphorylated form, is capable, under certain conditions, in the absence of protein, of catalyzing the reactions of decarboxylation, the formation of acetone, and the dismutation of diacetyl. Various variants of experiments in which the coenzymatic activity of TDP was compared with the activity of vitamin antimetabolites or studied with the addition of Reinecke's salt, bromoacetate, para-chloromercury-benzoate and other compounds showed that the catalytically most important groups in the thiamine molecule are: sulfur, quaternary nitrogen thiazole ring, amino group in position 4 of the pyrimidine ring, second carbon atom of thiazole (2-C-Tz), methylene bridge. Some active centers (sulfur, nitrogen, methylene bridge) are only necessary to maintain a certain structure and create an appropriate electron density at the second carbon atom of thiazole (2-C-Tz), which is the main catalytic center. Controversial and uncertain so far are the ideas about the meaning of the amino group of the pyrimidine component.

The value of the second carbon of thiazole

The catalytic properties of thiazolium salts were shown for the first time using benzoin condensation as an example. Then it was found that under normal, close to physiological conditions, a proton is easily split off from 2-C-Tz, and a double ion is formed from thiamine, for which it was easy to postulate the mechanisms of interaction with alpha-keto acids and the formation of an intermediate compound hydroxyethylthiamine (OET), corresponding to concept of "active acetaldehyde".

Synthetic drugs SP tested as growth factors for microbes had 80% potency compared to vitamin. The formation of WE as a natural metabolic product has been shown for some microorganisms. Ideas about the decisive role of 2-C-Tz in the implementation of coenzyme functions turned out to be quite fruitful, since in a relatively short period of time some TDP derivatives were also isolated, corresponding to other known intermediate products of enzymatic reactions: dihydroxyethyl-THD (“active glycol aldehyde” in the transketolase and phosphoketolase reactions), alpha-hydroxy-gamma-carboxy-propyl-TDF ("active succinic semialdehyde") and hydroxymethyl-TDF, which plays a role in the exchange of glyoxylate and the formation of active formyl radicals.

Significance of the pyrimidine component

Even minor substitutions in the aminopyrimidine component of thiamine sharply reduce the vitamin activity of new compounds. Particular attention in this regard has long been given to the amino group, the replacement of which by the hydroxy group causes the formation of the well-known vitamin antimetabolite oxy-T, which, after phosphorylation to diphosphate, can suppress the activity of both PD and TC. Loss of coenzyme activity is also observed in the case of minor changes structure of the amino group (methylation) or its simple removal from TDF.

A critical review of the extensive experimental material concerning the study of the catalytic activity of thiamine or its derivatives in model and enzyme systems forces us to pay new attention to certain features of the structure of the catalyst and the substrates exchanged with its participation.

Such a feature, common to the coenzyme and substrates, is the strict dependence of the reactions under consideration simultaneously on two active centers - on the substrate and, apparently, on the catalyst. Indeed, the entire variety of substrates involved in the reactions catalyzed by TDP can be easily reduced to a fundamentally unified type, a feature of which is the adjacent carbonyl and hydroxyl groups at neighboring carbon atoms. Only between such carbon atoms does the bond break (thiaminolysis) occur with the participation of TDF. In this case, the same fragment always becomes "active", capable of various condensations, and the second - "passive", the final metabolite of the reaction. A certain arrangement of the carbonyl and hydroxyl groups is absolutely necessary for the implementation of the catalytic mechanism.

Non-coenzymatic activity of thiamine and some of its derivatives

Along with elucidation of the mechanism of the main reactions in which TDP plays a catalytic role, there are numerous data on the high biological activity of other non-coenzymatic thiamine derivatives. Two directions of research have clearly emerged: the possible participation of various phosphoric esters of the vitamin in the active transfer of energy-rich phosphate groups (the anhydride bond in TDP is macroergic) and the possibility of thiamine intervening in redox reactions. Due to the fact that the specific thiamine-containing enzyme systems involved in the regulation of the processes mentioned above are unknown, the effects of the vitamin observed in this area of ​​metabolism can be considered as a manifestation of its nonspecific functions.

Thiamine phosphates (tf)

After development available methods To obtain TDP, it began to be widely tested in various diseases in clinical settings. Intravenous administration of 100-500 mg of TDP in diabetic acidosis increased the amount of pyruvate formed from glucose. An effect of a similar nature was observed in diabetes after the administration of ATP or phosphocreatine. In muscles during fatigue and rest, the breakdown and resynthesis of TDP occur approximately according to the same patterns that are known for ATP and phosphocreatine. Changes were characteristic during rest, when the amount of TDP exceeded the initial level before tiring work. The reasons for the enhanced breakdown of TDP during muscle contraction can hardly be explained from the standpoint of the known coenzyme functions of TDP. It has been established that the administration of large doses of TDP to animals after a few hours significantly (sometimes by 2 times) increases the content of labile phosphorus compounds in tissues.

Free thiamine and its derivatives

The administration of vitamin antimetabolites, oxy-T and PT, to animals causes a different pattern of disturbances in metabolism and in physiological functions, which made it possible to assume that thiamine may have several different or even independent functions. The difference between these antimetabolites from a chemical point of view is reduced to the exclusion of thiol disulfide transformations in PT and tricyclic thiochrome (Tx) type in oxy-T. The possibility of catalytic action of thiamine at the level of redox reactions in metabolism has long been admitted and criticized by various authors. Indeed, different availability of the vitamin strongly affects the activity of a number of oxidative enzymes or the content of reduced forms of glutathione in the blood. Vitamin has antioxidant properties in relation to ascorbic acid, pyridoxine and easily interacts with hydroxy groups of polyphenols. Dihydro-T is partially oxidized to thiamine by yeast and cell-free extracts, crystalline preparations of peroxidase, tyrosinase and non-enzymatically when interacting with crystalline ubiquinone, plastoquinone, menadione.

Thiol-disulfide transformations

TDS was found in animal tissues, urine, blood flowing from the liver perfused with the vitamin, yeast, etc. The ease of interaction of TDS with cysteine ​​and glutathione was the reason for the assumption that the vitamin in the form of thiol is directly involved in redox reactions in the body. It has also been shown that in an alkaline environment and in biological systems, the vitamin easily reacts with various thiol compounds, forming paired disulfides. When interacting with hydroquinone, rutin and catechins, thiamine turns into TDS. This reaction may play a special role in the reversible conversion of quinones to diphenols, for example, in melanogenesis at one of the stages of the conversion of tyrosine to melanin.

Participation of thiamine in metabolism

The decarboxylation of alpha-keto acids in microorganisms proceeds without conjugated oxidation, and the enzyme carboxylase, typical for this action, decomposes pyruvate to carbon dioxide and acetaldehyde.

CH3-CO-COOH --> CH3-CHO + CO2

The same enzyme takes part in the exchange of other similarly constructed keto acids and can catalyze the condensation of the resulting aldehydes to the corresponding acyloins. Non-oxidative transformations of alpha-keto acids under certain conditions also take place in animal tissues. But for animal tissues, the main typical way of converting alpha-keto acids is their oxidative decarboxylation. This process concerns several compounds (pyruvate, ketoglutarate, glyoxylate, gamma-hydroxy-alpha-ketoglutarate) and is associated with various specific enzymes.

1. Pyruvic acid dehydrogenase (PD) carries out the decarboxylation and oxidation of pyruvate (PA) through intermediate steps that can be summarized by the general equation:

CH3-CO-COOH + CoA + OVER CH3-CO-CoA + CO2 + OVERH2.

Thus, the reaction controls the process of aerobic oxidation of carbohydrates and occupies a key position in the conversion of carbohydrates to lipids and glucose catabolism through the citric acid cycle. The enzyme is very sensitive to a lack of thiamine in the whole body, and therefore beriberi and hypovitaminosis B1, as a rule, are accompanied by inhibition of the process of disintegration of PA and the corresponding accumulation of ketoacid in the blood and urine. The latter circumstance is widely used as a biochemical indicator of thiamine deficiency. The PD reaction is also of great importance in maintaining a certain balance in amino acid metabolism, since PC is a participant in many transamination reactions, as a result of which it is converted into the amino acid alanine.

2. Alpha-ketoglutaric acid dehydrogenase (AGD) in the main sequence of its action and the cofactors involved in the reaction does not differ from PD. However, the enzyme itself is built from larger protein subunits, and TDP in it is more tightly bound to the decarboxylating fragment than to the analogous protein in PD. This circumstance in itself largely explains the high resistance of the enzyme to thiamine deficiency in the body and emphasizes the importance of the reaction catalyzed by CHD for vital processes. Indeed, the enzyme, being a component of the cyclophorase system, is involved in the oxidative conversion of alpha-ketoglutaric acid (KGA) to succinyl-CoA.

HOOS-CH2 CH2 CO-COOH + CoA + OVER --> HOOS-CH2 CH2 CO-CoA + CO2 + OVER-H2.

The level of CHC, controlled by CHD, is also important for the implementation of a constant connection of the citric acid cycle with protein metabolism, in particular with the reactions of transamination and amination, which result in the formation of glutamic acid.

3. Gamma-hydroxy-alpha-ketoglutaric acid dehydrogenase was discovered in 1963. This compound is formed in tissues in noticeable amounts from hydroxyproline or from PA and glyoxylate. After oxidative decarboxylation, gamma-hydroxy-alpha-CHC is converted to malic acid, one of the intermediate substrates of the citric acid cycle. With thiamine deficiency, the enzyme quickly loses its activity, and the slow metabolism of PA observed under these conditions contributes to the excessive formation of gamma-hydroxy-alpha-CHC. The latter compound, as it turned out, is a powerful competitive inhibitor of aconitase, isocitrate dehydrogenase, and alpha-CHC dehydrogenase, i.e., three enzymes of the citric acid cycle at once. This circumstance quite well explains the fact that previously seemed contradictory, when the amount of CHD in B1 avitaminosis remains almost normal with a clear inhibition of the citric acid cycle.

4. Oxidative decarboxylation of glyoxylic acid with the formation of an active formyl residue, which, apparently, can be widely used in the corresponding exchange reactions, for example, in the synthesis of nitrogenous bases of nucleic acids.

5. Phosphoroclastic cleavage of ketosaccharides, in particular xylulose-5-phosphate in some microorganisms, is carried out by the TDP-containing enzyme phosphoketolase.

Xylulose-5-phosphate + H3PO4 --> phosphoglyceraldehyde + acetyl phosphate.

The absence of known specific hydrogen acceptors in the composition of this enzyme suggests that the DOETD formed during the reaction undergoes intramolecular oxidation with the formation of an acetyl residue immediately on TDP, after which the finished acetyl is removed from the coenzyme with the participation of phosphoric acid. Due to the fact that the reaction proceeds similarly with fructose-6-phosphate, it is assumed that microorganisms have a special “phosphoketolase” shunt in carbohydrate metabolism, which, with the participation of transaldolase, transketolase, isomerase and epimerase of pentose phosphates, aldolase and fructose diphosphatase, provides a shortened assimilation pathway fructose with the possible formation of 3 molecules of ATP and acetate.

Fructose-6-phosphate + 2H3PO4 --> 3-acetyl phosphate.

Enzymes similar to phosphoketolase catalyzing the formation of acetyl phosphate from pyruvate have also been found in certain types of microorganisms.

6. Transketolase catalyzes the reactions of glycolaldehyde radical transfer from ketosaccharides to aldosaccharides. A typical and perhaps the most important example of this kind is the interaction of xylulose-5-phosphate with ribose-5-phosphate or with erythrose-4-phosphate in the pentose cycle. With the participation of transketolase, reactions of non-oxidative formation of pentose phosphates from hexose phosphates or reactions of assimilation of pentose phosphates occur when it comes to the functioning of the glucose-monophosphate oxidative shunt. Obviously, in this way, the processes of providing the body with pentose phosphates (synthesis of nucleotides, nucleic acids) and NADPH2, which is the most important supplier of hydrogen in most reductive biosynthesis (fatty acids, cholesterol, hormones, etc.), are closely related to transketolase. The same transketolase reaction serves as one of the intermediate steps in the processes of photosynthesis, depending on the constant regeneration of ribulose-1,5-diphosphate. It is interesting to note that DOETDP, which appears during the transketolase reaction, turned out to be a compound that undergoes oxidation to glycolyl-CoA in the alpha-ketoacid dehydrogenase system. In this way, a residue of glycolic acid can arise, which is then used in the synthesis of N-glycolyl-neuraminic acid and other glycol compounds.

Antithiamine factors

• vitamin antimetabolites
• substances that inactivate the vitamin in different ways by interacting directly with it.

The first group covers a number of artificially obtained analogs of thiamine with various chemical modifications of the structure of its molecule. The interest in such compounds is explained by the fact that some of them turned out to be powerful antiprotozoal drugs, while others cause changes in the body of animals that are of interest for the correction of individual metabolic disorders in humans.

The second group includes enzymes that specifically destroy vitamin (thiaminases), and very diverse natural compounds (thermostable antivitamin factors) that inactivate thiamine. Antivitamins of the second type in some cases act as pathogenetic agents in the development of hypo- and avitaminosis conditions in humans or animals and, possibly, play a certain role as natural regulators of thiamine action. Consideration of the issue in this regard seems reasonable due to the fact that an excess of the vitamin in the body leads to distinct metabolic abnormalities, and some diseases in humans are accompanied by the accumulation of thiamine not only in the blood, but also in the internal organs.

Thiamine antimetabolites

The significance of the pyrimidine and thiazole components in enzymatic reactions and the role of the hydroxyethyl radical for TDP fixation in tissues or for participation in rephosphorylation reactions have been discussed above in detail. All three listed groups turned out to be those parts of the vitamin molecule, modifications of which dramatically change the biological properties of the entire compound. Of the derivatives with a modified thiazole structure, the analogue in which the thiazole is substituted by pyridine, PT, has been most studied. The antivitamin properties of this compound in relation to nervous tissue can be enhanced by about 10 times if the 2 "-methyl group in pyrimidine is simultaneously replaced with ethyl. -butyl-T. Researchers came to the production of antimetabolites with a modified 5-hydroxyethyl radical in a roundabout way. Initially, 1-(4-amino-2-p-propyl-5-pyrimidinyl)-2-picoline chloride or amprol was obtained, which turned out to be a very effective anticoccidiosis drug. Then it turned out that its therapeutic effect is due to a violation of the assimilation (most likely phosphorylation) of thiamine in protozoa. The derivatives of the vitamin obtained after this, devoid of hydroxyl in the 5-ethyl radical, became a new group of antimetabolites produced on an industrial scale for medicinal purposes.

Natural Antivitamin Factors

Thiaminase. Symptoms resembling the paralytic form of beriberi and appearing in foxes with their predominant feeding of raw carp were first described in 1936. It was soon established that the cause of the disease in animals was thiamine deficiency, caused by the presence in the internal organs of carp and other tissues of some marine fish, mollusks, plants and microorganisms of an enzyme that specifically destroys thiamine - thiaminase. Later, two forms of the enzyme began to be distinguished: thiaminase I, which cleaves the vitamin with the simultaneous replacement of thiazole with some nitrogenous base, and thiaminase II, which hydrolytically destroys the vitamin into pyrimidine and thiazole components. The second form of thiaminase has so far been found only in microorganisms (Bac. aneurinolyticus), but the latter are often the cause of thiaminase disease in humans, which occurs as chronic hypovitaminosis B1.

Thermostable factors that inactivate thiamine have been found in fish and in many plants, especially ferns. Often these factors are associated with thiaminases. It is known that the thermostable factor from the insides of carp destroys the vitamin, like thiaminase, and is itself a substance of hemic nature, and the factor contained in the fern is 3,4-dihydroxycinnamic acid, which forms inactive complexes with thiamine.

Both thiamine antimetabolites and natural antivitamin factors are widely used for experimental reproduction of B1 beriberi in animals, and some of them (amprol, chlorothiamine) are used as medicinal preparations in veterinary practice.

The need for thiamine and methods for determining the provision of the body with vitamin B1

Difficulties in determining the need for thiamine in humans or animals are mainly due to the impossibility of conducting appropriate balance experiments for these purposes, since a significant proportion of the vitamin entering the body undergoes numerous transformations that are still poorly understood. In this regard, the only criterion that is the control of the vitamin value of the diet are indirect indicators determined by the analysis of urine and blood in humans or even tissues in animals. Much of the advice on thiamine requirements is based on an assessment general condition examined: the absence of clinical signs of hypovitaminosis, the elimination of certain types of functional deficiency by additional administration of the vitamin, etc. For the Russian population, taking into account adjustments for individual fluctuations, a norm of 0.6 mg of thiamine per 1000 cal of the daily diet is recommended. This dose should be considered as the most fully taking into account the human need for vitamin in the conditions of average climatic zones and average physical activity. Within certain limits, the professional features of diets (increase in calories) with this approach are provided by a set of various products in the food consumed per day. However, it must be remembered that the predominance of fats in the diet (4 times against the usual) reduces the need for thiamine by about 15-20%, and excess carbohydrate intake, on the contrary, increases the consumption of the vitamin.

It is known that the need for thiamine in relation to the calorie content of food increases with physical and neuropsychic stress, during pregnancy and lactation, when the body is exposed to certain chemical (drugs, industrial poisons) or physical (cooling, overheating, vibration, etc.) factors, as well as in many infectious and somatic diseases. Thus, the need for thiamine in the conditions of the Far North is 30-50% higher. With the aging of the body, when the conditions for absorption and interstitial assimilation of the vitamin noticeably worsen, the calculation of the need should be increased by 25-50% in relation to the calorie content of food. Dramatically (by 1.5-2.5 times) the consumption of vitamin increases among workers of hot shops, flight personnel of modern high-speed aviation. With physiological stress caused by endogenous factors (pregnancy, lactation), the need for thiamine increases by 20-40%. With many intoxications and diseases, daily administration of thiamine is recommended in doses many times higher than the physiological need (10-50 mg). It is unlikely that in the latter cases we are talking about the specific vitamin action of the administered compound, since certain properties of thiamine as a chemical compound can play a special role in this case.

Daily requirement for thiamine of various population groups in cities with developed public services
(In cities and villages with less developed public services, the need increases by about 8-15%)
by labor intensity

		Thiamine requirement in mcg
Groups	Age in years	Men		Women
		under normal conditions		under normal conditions	with additional physical activity
First	18 - 40	1,7	1,9	1,4	1,6
	40 - 60	1,6	1,7	1,3	1,4
Second	18 - 40	1,8	2,0	1,5	1,7
	40 - 60	1,7	1,8	1,4	1,5
Third	18 - 40	1,9	2,1	1,5	1,8
	40 - 60	1,7	1,9	1,6	1,6
Fourth	18 - 40	2,2	2,4	2,0	2,0
	40 - 60	2,0	2,2	1,7	1,8
Youths	14 - 17	1,9
Girls	14 - 17			1,7
Elderly	60 - 70	1,4	1,5	1,2	1,3
old	70	1,3		1,1
Children (no gender division)
Children	0,5 - 1,0	0,5
Children	1 - 1,5	0,8
Children	1,5 - 2	0,9
Children	3 - 4	1,1
Children	5 - 6	1,2
Children	7 - 10	1,4
Children	11 - 13	1,7

For the most commonly used laboratory animals in the experiment, you can focus on the following thiamine requirements: for a pigeon - 0.125 mg per 100 g of feed, for a dog - 0.027-0.075 mg, for a mouse - 5-10 mcg, for a rat - 20-60 mcg , for a cat - 50 mcg per 100 g per day.

Thus, the decisive criterion for the provision of the body with thiamine is the reliability of determining the presence or absence of vitamin deficiency in the subjects. Important indicators, along with the determination of the vitamin itself, in this case are metabolites (alpha-keto acids), the exchange of which depends on TDP-containing enzymes, or the enzymes themselves (dehydrogenases, transketolase). Taking into account the specifics of clinical and experimental studies, let us briefly consider the value of the listed indicators in application to some specific conditions and the nature of the material being analyzed.

Urinalysis

As already noted, in humans, the content of the vitamin in daily urine is less than 100 μg, which is accepted by most authors as evidence of thiamine deficiency. However, with a normal intake of the vitamin with food, its excretion in the urine also depends on the nature of the drug treatment (if we are talking about the patient) and the state of the excretory function of the kidneys. Certain medications can dramatically reduce, while others increase the excretion of the vitamin. Increased excretion of thiamine cannot always be taken as evidence of vitamin saturation, since the cause may be a violation of the mechanisms of reabsorption in the tubular apparatus of the kidneys or insufficient deposition of the vitamin due to a violation of its phosphorylation processes. On the other hand, the low content of thiamine in the urine of sick people may not be due to its deficiency, but the result of a partial restriction of food intake, containing a correspondingly smaller amount of vitamin. For this reason, in order to obtain additional information about the state of interstitial metabolism of thiamine, the method of examining urine after parenteral loads is quite widespread. It is convenient to carry out a threefold load, based on a dose of 0.5 mg of vitamin per 1 kg of the patient's weight, rounding the weight to tens of kilograms.

All methods for the determination of thiamine must be checked for the reproducibility of the values ​​obtained with their help in the presence of drugs in the urine of patients. It is known, for example, that salicylates, quinine, and other preparations can cause additional fluorescence, interfering with the correct interpretation of fluorometry data, while PASA, interacting directly with ferricyanide, sharply reduces the yield of thiochrome. Under experimental conditions, a convenient indicator of thiamine availability is the determination of the level of pyruvate (PK) in the urine. It must be remembered that only pronounced forms of hypovitaminosis B1 are accompanied by a distinct accumulation of this keto acid, which is most often defined as bisulfite-binding substances (BSV). In pathological conditions, especially when it comes to sick people, the level of BSF, as well as the amount of PA itself in the urine, varies over a very wide range depending on the intensity of carbohydrate metabolism, and the latter is controlled by a large number of different factors that are not directly related to thiamine. Indicators of the level of BSF or PC in the urine in such situations should be used only as additional data.

Blood test

The main form of the vitamin present in the blood is TDP. Definitions made in healthy people various methods, give on average the same values, but with fluctuations in a fairly wide range (4-12 μg%). As a reliable sign of vitamin deficiency, if you focus only on this indicator, you can consider only values ​​​​below 2-4 μg%. Less acceptable is the determination of total thiamine alone. Normally, this does not introduce a significant error, since there is very little free vitamin - 0.3-0.9 μg%. Its amount in the blood serum can increase sharply with a deterioration in the excretory function of the kidneys in hypertension or due to a violation of the process of vitamin phosphorylation. If the above restrictions are absent, then we can assume that the level of thiamine in the blood adequately reflects the provision of the body with it.

In the study of blood, as well as urine, the determination of the concentration of PC is widely used. It is important to use a more specific method for these purposes (enzymatic, chromatographic), since reactions with bisulfite or salicylic aldehyde give overestimated results. If PC is determined to characterize the metabolism of a vitamin in patients, it is necessary to take into account a large number of factors that are not related to this vitamin, but actively affect the metabolism, and, consequently, the level of PC in the body. Thus, an increase in the level of blood PC is observed with the introduction of adrenaline, ACTH, during exercise, electrical and insulin shock, vitamin A and D deficiency, many infectious and other diseases, when it is often difficult to suspect thiamine deficiency. The experiment showed that in a number of cases the level of blood PC correlates more with the hyperfunction of the pituitary-adrenal cortex system than with the provision of the body with vitamin.

Since there are difficulties in identifying the true state of thiamine metabolism by the content of the vitamin itself in the blood or the level of keto acids, it is possible to use for these purposes the determination of the activity of TDP-containing enzymes, in particular transketolase (TK) of erythrocytes. For this enzyme, even minor shifts in the concentration of the coenzyme significantly affect the activity of the entire system. Observations in the clinic and during preventive examinations of the population, experiments on animals confirm the very high sensitivity of TC even to mild vitamin deficiency. The enzyme reacts even when changes in the level of PC or the vitamin itself in the blood are not indicative. For greater accuracy, the method of additional activation of TA added in vitro to the hemolysate of erythrocytes with TDF is now used. Stimulation of the TC up to 15% of the initial activity is taken according to the norm, from 15 to 25% - hypovitaminosis, more than 20-25% - beriberi.

Violation of vitamin balance and thiamine metabolism

Widespread in the 19th and early 20th centuries in countries Far East disease (beriberi), which is a classic form of vitamin B1 deficiency, is now much less common. There are three forms of beriberi, corresponding to the most pronounced manifestations of the disease:

• dry, or paralytic (neurological lesions predominate - paresis, paralysis, etc.);
• edematous (disturbances are observed mainly on the part of the circulatory apparatus of the blood);
• acute, or cardiac (rapidly ends in death against the background of severe right ventricular failure).

Practically listed forms in pure form are rare, and their partial mutual transitions are observed. In modern conditions, hypovitaminosis B1 of various depths is most common. The symptoms of the latter are, as a rule, quite general (shortness of breath, palpitations, pain in the region of the heart, weakness, fatigue, loss of appetite, decrease in overall resistance to other diseases, etc.) and cannot be fully recognized as typical for insufficiency only thiamine, as it occurs in many other hypovitaminosis. In essence, it should be stated once again that the listed symptoms can be finally attributed to hypovitaminosis B1 only on the basis of special biochemical studies (see above). Secondary hypovitaminosis B1, which occurs as a result of an imbalance or vitamin metabolism, requires separate consideration. The first group should include cases of increased consumption of the vitamin during its usual intake with food (thyrotoxicosis and some other diseases, excess carbohydrates in the diet), impaired absorption from the gastrointestinal tract or increased excretion of the vitamin into the urine after long-term use of diuretics. The second group of disorders is associated by most authors with a weakening of the processes of interstitial phosphorylation of thiamine or its proteidization, as in the therapeutic use of isonicotinic acid hydrazides or protein starvation.

The variety of causes listed above (essentially of an endogenous order) determines the development of thiamine deficiency, which is largely eliminated in the first group of disorders by additional administration of the vitamin in high doses. Hypovitaminoses of the second type are often not amenable to direct vitamin therapy and require preliminary elimination of the initial basic disorders in the metabolism of thiamine itself or the introduction of coenzyme derivatives into the body.

Combining such etiologically different forms of thiamine deficiency in the body into one group of so-called endogenous hypovitaminosis does not seem to be entirely successful. For violations of the metabolic order, the term "dysvitaminosis" is more appropriate, that is, simply a statement of the fact of a violation of vitamin metabolism with its normal, sufficient intake into the body. Something similar is observed when vitamins compete with each other, when an excessive intake of one of the vitamins inhibits the metabolism and proteinization of the other.

Preventive and curative use of thiamine and its derivatives

Indications and contraindications for thiamine therapy

When substantiating the main principles of the therapeutic use of a vitamin or its derivatives, one has to proceed from several premises. In the case when it comes to deficiency by the type of beriberi or hypovitaminosis, treatment is carried out according to the usual rules. replacement therapy. The situation is more complicated with dysvitaminoses that occur against the background of any pathological process or as a result of the impact on the metabolism of thiamine of various exogenous factors (medicines, chemical poisons, physical agents, etc.), when success largely depends on etiotropic therapy or the use of appropriate vitamin preparations (cocarboxylase, disulfide derivatives). Analyzing the available data, we can assume that the prerequisites for medicinal use thiamine are available for various etiology lesions of the gastrointestinal tract, liver, neuropsychiatric diseases, cardiovascular insufficiency, hypotension, rheumatism. Practical experience justifies the use of the vitamin in rickets, chronic tonsillitis, many skin and infectious diseases, diabetes, hyperthyroidism, tuberculosis. Sufficiently justified is the prophylactic administration of thiamine to athletes, pilots on the eve of the expected overload, workers dealing with industrial poisons (carbon monoxide, ammonia, nitrogen oxides, etc.), in obstetric practice on the eve of childbirth and in other cases.

The second direction in substantiating thiamine therapy may be taking into account the known biochemical functions of this vitamin. In this case, the issue must be resolved on the basis of specific data on the violation in the patient's body of those metabolic processes that we can correct with the introduction of the vitamin. In essence, we should talk about the coenzymatic and non-coenzymatic activity of thiamine, i.e., about those of its functions that are discussed in detail above. Initially, the main indications for the use of thiamine in various diseases were symptoms typical of beriberi: neuritis, neuralgia, paralysis, pain of various etiologies, disorders of nervous and cardiac activity. Currently, when justifying the need for vitamin therapy, they mainly proceed from metabolic disorders (acidosis, diabetic coma, pyruvatemia, toxemia of pregnant women).

Thiamine is used for peripheral neuritis, general disorders due to malnutrition, anorexia, Wernicke's encephalopathy, vitamin deficiency, chronic alcoholism, alcoholic neuritis, cardiovascular insufficiency, disruption of the gastrointestinal tract.

In all of these diseases (except Wernicke's encephalopathy), thiamine is approximately equally used enterally and parenterally in doses ranging from 5 to 100 mg per day. Currently, some therapeutic vitamin preparations are widely introduced into clinical practice: thiamine phosphates (TF) and disulfide derivatives. After the development of a simple method for the synthetic production of TF, the so-called cocarboxylase (TDF) quickly gained popularity as a therapeutic drug. The reason for the introduction of TDF into medical practice was the well-known fact of the coenzyme activity of this particular vitamin derivative. In addition, the toxicity of TF is 2.5-4 times less than that of free thiamine. There is another significant advantage of TF - more complete digestibility. So in humans, after equimolar intramuscular injections of thiamine, TMF and TDP, the amount of vitamin found in the urine in 24 hours was 33, 12 and 7% of the administered dose, respectively.

The use of TF is most effective in cases where it is necessary to carry out vitamin therapy in patients with weakened phosphorylation processes. So, with pulmonary tuberculosis, thiamine injections are ineffective: up to 70% of the vitamin can be excreted in the urine per day. If patients received equivalent doses of TDP, then the excretion of the vitamin from the body was less - 11%. When administered parenterally, especially intravenously, TDF gives metabolic effects that are not observed after injections of free vitamin. Very often, TDP causes shifts similar to those observed with the use of ATP or phosphocreatine.

The most numerous data concerning the use of TDF in diabetes mellitus and cardiovascular insufficiency. The appointment of TDF (50-100 mg intravenously) dramatically reduced mortality from diabetic coma and turned out to be very effective tool in the treatment of acidotic conditions. TDF not only enhances the action of insulin, but also relieves insulin resistance in some patients. Along with the normalization of traditional indicators characterizing the severity of diabetes mellitus (glycemia, glucosuria, ketosis), TDF has a clear normalizing effect on the level of cholesterol and corvi phospholipids. In case of cardiovascular insufficiency, even single injections of TDP quickly normalize elevated levels of pyruvate and lactic acid in the blood of patients.

TDP markedly activates myocardial uptake nutrients from the blood, quickly improving the electrocardiogram. A similar effect of TDP is widely used in the treatment of various functional anomalies of the heart (extrasystole, some forms of arrhythmias). Pronounced positive changes in electrocardiogram parameters in artherosclerosis, hypertension, some endocrine and renal diseases, myocardial infarction, and heart valve defects are described in cases where the leading factor in the pathology was a violation of heart trophism. It has also been shown that TDP is more effective than thiamine in diseases of the peripheral and central nervous system, with multiple sclerosis, bronchial asthma and many other diseases.

Various disulfide derivatives of the vitamin are also widely used, the effectiveness of which is explained by the better absorption of disulfide forms in the intestinal tract. One of the advantages of these derivatives is their significantly lower toxicity compared to thiamine.

B 1 contains sulfur atoms, which is why it was named thiamine. Its chemical structure contains two rings - pyrimidine and thiazole, connected by a methylene bond. Both ring systems are synthesized separately as phosphorylated forms, then combined via a quaternary nitrogen atom.

Thiamine is highly soluble in water. Aqueous solutions of thiamine in an acidic environment withstand heating to high temperatures without reducing biological activity. In a neutral and especially in an alkaline environment, vitamin B 1, on the contrary, is quickly destroyed when heated. This explains the partial or even complete destruction of thiamine during culinary processing of food, such as baking dough with the addition of sodium bicarbonate or ammonium carbonate. When thiamine is oxidized, thiochromium is formed, which gives blue fluorescence under UV irradiation. This property of thiamine is based on its quantitative determination.

Vitamin B 1 is easily absorbed in the intestines, but does not accumulate in tissues and does not have toxic properties. Excess dietary thiamine is rapidly excreted in the urine. The conversion of vitamin B 1 to its active form, thiamine pyrophosphate (TPP), also called thiamine diphosphate (TDP), involves the specific ATP-dependent enzyme thiamine pyrophosphokinase, which is found mainly in the liver and brain tissue. Experiments with labeled 32 P ATP proved the transfer of the entire pyrophosphate group to thiamine in the presence of the enzyme. TPP has the following structure:

If vitamin B 1 is supplied with food in the form of TPP, then the pyrophosphate group is cleaved from it under the action of intestinal pyrophosphatases.

In the absence or insufficiency of thiamine, a serious disease develops - beriberi, which is widespread in a number of countries in Asia and Indochina, where rice is the main food. It should be noted that vitamin B1 deficiency also occurs in European countries, where it is known as Wernicke's symptom, which manifests itself in the form of encephalopathy, or Weiss syndrome with a predominant lesion of the cardiovascular system. Specific symptoms are associated with primary disorders of the activity of both the cardiovascular and nervous systems, as well as the digestive tract. The point of view is currently being reconsidered that beriberi in humans is the result of a deficiency of only vitamin B 1 . It is more likely that this disease is a combined avitaminosis or polyavitaminosis, in which the body also lacks riboflavin, pyridoxine, vitamins PP, C, etc. Experimental avitaminosis B l was obtained on animals and volunteers. Depending on the predominance of certain symptoms, a number of clinical types of insufficiency are distinguished, in particular, the polyneuritic (dry) form of beriberi, in which disturbances in the peripheral nervous system come to the fore. With the so-called edematous form of beriberi, the cardiovascular system is predominantly affected, although polyneuritis is also noted. Finally, an acute cardiac form of the disease, called pernicious, is isolated, which leads to death as a result of the development of acute heart failure. In connection with the introduction of a crystalline thiamine preparation into medical practice, mortality has sharply decreased and rational ways have been outlined for the treatment and prevention of this disease.

The earliest symptoms of avitaminosis B 1 include disturbances in the motor and secretory functions of the digestive tract: loss of appetite, slowing down of peristalsis (atony) of the intestine, as well as changes in the psyche, consisting in loss of memory for recent events, a tendency to hallucinations; there are changes in the activity of the cardiovascular system: shortness of breath, palpitations, pain in the region of the heart. With the further development of beriberi, symptoms of damage to the peripheral nervous system (degenerative changes in nerve endings and conductive bundles) are revealed, expressed in sensitivity disorder, tingling sensation, numbness and pain along the nerves. These lesions end with contractures, atrophy and paralysis of the lower and then upper limbs. In the same period, the phenomena of heart failure develop (increased rhythm, boring pains in the region of the heart). Biochemical disorders in avitaminosis B 1 are manifested by the development of a negative nitrogen balance, the excretion of amino acids and creatine in increased amounts in the urine, the accumulation of α-keto acids and pentose sugars in the blood and tissues. The content of thiamine and TPP in the heart muscle and liver in patients with beriberi is 5-6 times lower than normal.

biological role. It has been experimentally proven that vitamin B 1 in the form of TPP is integral part at least 5 enzymes involved in intermediate metabolism. TPP is part of two complex enzyme systems - pyruvate- And α - ketoglutarate dehydrogenase complexes, catalyzing oxidative decarboxylation pyruvic and α-ketoglutaric acids. As part of transketolase, TPP is involved in the transfer of the glycoaldehyde radical from ketosaccharides to aldosaccharides (see Chapter 10). TPP is