Food proteins are the main source of nitrogen for the body. Nitrogen is excreted from the body in the form of end products of nitrogen metabolism. The state of nitrogen metabolism is characterized by the concept of nitrogen balance.

Nitrogen balance– the difference between nitrogen entering the body and leaving the body. There are three types of nitrogen balance: nitrogen balance, positive nitrogen balance, negative nitrogen balance

At positive nitrogen balance nitrogen intake prevails over its release. Under physiological conditions, a true positive nitrogen balance occurs (pregnancy, lactation, childhood). For children aged 1 year of life it is +30%, at 4 years old - +25%, in adolescence +14%. With kidney disease, a false positive nitrogen balance is possible, in which the end products of nitrogen metabolism are retained in the body.

At negative nitrogen balance The release of nitrogen predominates over its intake. This condition is possible with diseases such as tuberculosis, rheumatism, oncological diseases. Nitrogen balance typical for healthy adults whose nitrogen intake is equal to its excretion.

Nitrogen metabolism is characterized wear coefficient, which is understood as the amount of protein that is lost from the body under conditions of complete protein starvation. For an adult, it is 53 mg/kg (or 24 g/day). In newborns, the wear rate is higher and is 120 mg/kg. Nitrogen balance is ensured by protein nutrition.

Protein diet characterized by certain quantitative and qualitative criteria.

Quantitative criteria for protein nutrition

Protein minimum- the amount of protein that ensures nitrogen balance, provided that all energy costs are provided by carbohydrates and fats. It is 40-45 g/day. With prolonged use of a protein minimum, immune processes, hematopoietic processes, and the reproductive system suffer. Therefore, for adults it is necessary protein optimum - the amount of protein that ensures the performance of all its functions without compromising health. It is 100 – 120 g/day.

For children The consumption rate is currently being revised towards its reduction. For a newborn, the need for proteins is about 2 g/kg, by the end of 1 year it decreases with natural feeding to 1 g/day, with artificial feeding it remains within 1.5 - 2 g/day

Qualitative criteria for protein nutrition

Proteins that are more valuable to the body must meet the following requirements:

• contain a set of all essential amino acids (valine, leucine, isoleucine, threonine, methionine, lysine, arginine, histidine, tryptophan, phenylalanine).
• the ratio between amino acids should be close to their ratio in tissue proteins
• well digested in the gastrointestinal tract

These requirements are best met by proteins of animal origin. For newborns, all proteins must be complete (proteins breast milk). At the age of 3-4 years, about 70-75% should be complete proteins. For adults, their share should be about 50%.

see Nitrogen minimum.

View value Physiological Minimum Protein in other dictionaries

Minimum- the least (the smallest)
at least (at least)
little by little
at the very least
Synonym dictionary

Squirrel- squirrels, w. A small forest animal - a rodent.
Ushakov's Explanatory Dictionary

Minimum- m. lat. least amount, magnitude, value, limit of what; opposite sex maximum, greatest.
Dahl's Explanatory Dictionary

Minimum- minimum, m. (Latin minimum) (book). 1. Smallest value; opposite maximum. atmospheric pressure. wages. Living wage (minimum means, money required........
Ushakov's Explanatory Dictionary

Physiological- physiological, physiological. 1. Adj. to physiology in 1 value. Physiological processes. Physiological chemistry. 2. transfer Roughly sensual.
Ushakov's Explanatory Dictionary

Belka J.— 1. A small fur-bearing animal of the rodent order, living in trees. 2. Fur, the skin of such an animal.
Explanatory Dictionary by Efremova

At Least Adv.- 1. At the very least.
Explanatory Dictionary by Efremova

Physiological Adj.— 1. Correlative in meaning. with noun: physiology, physiologist associated with them. 2. Characteristic of physiology (1), characteristic of it. 3. Associated with physiology (2), with life........
Explanatory Dictionary by Efremova

Squirrel- -And; pl. genus. -lock, dat. -lkam; and.
1. A small fur-bearing animal of the rodent order with a large fluffy tail, living in trees. Manual b. Spins (spins) like b. in the wheel.......
Kuznetsov's Explanatory Dictionary

Minimum- [lat. minimum].
I. -a; m.
1. The smallest quantity, the smallest value in a data series (opposite: maximum). The work requires a lot of equipment.
2. what or with def. Totality........
Kuznetsov's Explanatory Dictionary

Maximum and Minimum Interest Rate— (Collar) Simultaneous
buy at the top
limit and
selling at a lower limit to keep the interest rate within certain
borders.
Sales income........
Economic dictionary

Minimum— - 1. smallest value, smallest
size; 2.
the body of specialized knowledge required for
work in any field.
Economic dictionary

Minimum Double- a chart of changes in the price of securities, according to which the rate drops twice to its minimum level and rises again. When analyzing the state of the market M.D. means........
Economic dictionary

Minimum Wage— the level of wages of an unskilled worker.
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Minimum Cost- an optimality criterion, according to which a certain volume of production is fixed, and all calculations are carried out on the basis of obtaining a given volume with the least......
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Minimum Non-taxable- the amount of taxation below which the object is not subject to tax.
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Minimum Subsistence- level of income that provides
acquisition
a set of material goods and services necessary to ensure human life under a certain socio-economic........
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Minimum Subsistence Tax Free- the amount of funds necessary to satisfy the basic needs of a person, which is deducted from the taxable amount of income. In this capacity it can act........
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Minimum, Non-taxable— - the value of the taxable object, below which the object is not subject to tax.
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Non-taxable Minimum- minimal
tax-free income.
Economic dictionary

Tax Free Living Wage— See minimum living wage, tax-free
Economic dictionary

Living wage- the cost of the minimum set of goods necessary for a person, the means of subsistence that allow him to maintain life.
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Living wage (social and physiological)— - a set of goods and services expressed in monetary form and intended to satisfy physical needs, social and spiritual needs, which......
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Living Minimum Population- - cost
assessment of natural
a set of food products necessary to maintain human life at a physically low level, as well as expenses........
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Squirrel— Old Russian formation from the noun Bela. This animal, oddly enough, was named after the color of its skin, not of an ordinary animal well known to us, but by......
Krylov's etymological dictionary

Physiological- oh, oh.
1. to Physiology (1 mark). Fth research methods.
2. Associated with the physiology of the body, with its vital functions, based on them. F properties of animals. F.........
Kuznetsov's Explanatory Dictionary

Qualification Minimum- a minimum list of issues, legislative and regulatory documents, knowledge of which is mandatory for the qualified implementation of professional activities........
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Minimum Subsistence- level of income that ensures the acquisition of a set of material goods and services necessary to ensure human life under a certain socio-economic......
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Non-taxable Minimum— - minimum tax-free income.
Legal Dictionary

Nitrogen Minimum— (syn. physiological minimum protein) the smallest amount of protein introduced with food, at which nitrogen balance is maintained.
Large medical dictionary

Physiological minimum protein

1. Small medical encyclopedia. - M.: Medical encyclopedia. 1991-96 2. First aid. - M.: Great Russian Encyclopedia. 1994 3. Encyclopedic Dictionary of Medical Terms. - M.: Soviet Encyclopedia. - 1982-1984.

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- (syn. physiological minimum protein) the smallest amount of protein introduced with food, at which nitrogen balance is maintained ... Medical encyclopedia

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CHILDREN- CHILDREN. Contents: I. Definition of the concept. Changes in the body during R. Causes of R.................................................. 109 II. Clinical course of physiological R. 132 Sh. Mechanics R. ................. 152 IV. Maintaining R......................... 169 V … Great Medical Encyclopedia

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Proteins are an essential component of food. Unlike proteins, carbohydrates and fats are not essential components of food. About 100 grams of protein are consumed daily by a healthy adult. Dietary proteins are the main source of nitrogen for the body. In economic terms, proteins are the most expensive food component. Therefore, the establishment of protein standards in nutrition was very important in the history of biochemistry and medicine.

In the experiments of Karl Voith, the norms for the consumption of dietary protein were first established - 118 g / day, carbohydrates - 500 g / day, fats 56 g / day. M. Rubner was the first to determine that 75% of the nitrogen in the body is found in proteins. He compiled a nitrogen balance (determined how much nitrogen a person loses per day and how much nitrogen is added).

In an adult healthy person there is nitrogen balance - “zero nitrogen balance”(the daily amount of nitrogen excreted from the body corresponds to the amount absorbed).

Positive nitrogen balance(the daily amount of nitrogen excreted from the body is less than the amount absorbed). It is observed only in a growing body or during the restoration of protein structures (for example, during the recovery period from serious illnesses or when building muscle mass).

Negative nitrogen balance(the daily amount of nitrogen excreted from the body is higher than the amount absorbed). It is observed with protein deficiency in the body. Reasons: insufficient amount of protein in food; diseases accompanied by increased destruction of proteins.

In the history of biochemistry, experiments were carried out when a person was fed only carbohydrates and fats (“protein-free diet”). Under these conditions, nitrogen balance was measured. After a few days, the excretion of nitrogen from the body decreased to a certain value, and after that it was maintained for a long time at a constant level: a person lost 53 mg of nitrogen per kg of body weight per day (approximately 4 g of nitrogen per day). This amount of nitrogen corresponds to approximately 23-25g of protein per day. This value was called "WEAR RATIO". Then 10 g of protein was added to the diet daily, and nitrogen excretion increased. But a negative nitrogen balance was still observed. Then they began to add 40-45-50 grams of protein per day to food. With such a protein content in food, a zero nitrogen balance (nitrogen balance) was observed. This value (40-50 grams of protein per day) was called the PHYSIOLOGICAL MINIMUM OF PROTEIN.

In 1951, dietary protein standards were proposed: 110-120 grams of protein per day.

It has now been established that 8 amino acids are essential. The daily requirement for each essential amino acid is 1-1.5 grams, and the body needs 6-9 grams of essential amino acids per day in total. The content of essential amino acids varies among different foods. Therefore, the physiological minimum protein may be different for different products.

How much protein do you need to eat to maintain nitrogen balance? 20 gr. egg white, or 26-27 gr. meat or milk proteins, or 30 gr. potato proteins, or 67 gr. wheat flour proteins. Egg white contains a complete set of amino acids. When eating plant proteins, much more protein is needed to replenish the physiological minimum. Protein requirements for women (58 grams per day) are less than for men (70 g of protein per day) - data from US standards.

Nitrogen balance nitrogen balance.

The remaining amino acids are easily synthesized in cells and are called non-essential. These include glycine, aspartic acid, asparagine, glutamic acid, glutamine, serine, proline, alanine.

However, a protein-free diet ends in the death of the body. The exclusion of even one essential amino acid from the diet leads to incomplete absorption of other amino acids and is accompanied by the development of a negative nitrogen balance, exhaustion, stunted growth and dysfunction of the nervous system.

With a protein-free diet, 4g of nitrogen is released per day, which is 25g of protein (WEAR RATIO).

Physiological protein minimum - the minimum amount of protein in food necessary to maintain nitrogen balance is 30-50 g / day.

DIGESTION OF PROTEINS IN THE GASTROINTESTINAL TRACT. CHARACTERISTICS OF STOMACH PEPTIDASES, FORMATION AND ROLE OF HOLARIC ACID.

The content of free amino acids in food products is very low. The vast majority of them are part of proteins that are hydrolyzed in the gastrointestinal tract under the action of protease enzymes). The substrate specificity of these enzymes lies in the fact that each of them cleaves peptide bonds formed by certain amino acids at the highest speed. Proteases that hydrolyze peptide bonds inside a protein molecule belong to the group of endopeptidases. Enzymes belonging to the group of exopeptidases hydrolyze the peptide bond formed by terminal amino acids. Under the influence of all gastrointestinal proteases, food proteins break down into individual amino acids, which then enter tissue cells.

Formation and role of hydrochloric acid

The main digestive function of the stomach is that it begins the digestion of protein. Plays a significant role in this process hydrochloric acid. Proteins entering the stomach stimulate secretion histamine and groups of protein hormones - gastrinov, which, in turn, cause the secretion of HCI and the proenzyme pepsinogen. HCI is formed in the parietal cells of the gastric glands

The source of H + is H 2 CO 3, which is formed in the parietal cells of the stomach from CO 2 diffusing from the blood and H 2 O under the action of the enzyme carbonic anhydrase

Dissociation of H 2 CO 3 leads to the formation of bicarbonate, which is released into the plasma with the participation of special proteins. C1 ions enter the lumen of the stomach through the chloride channel.

The pH drops to 1.0-2.0.

Under the influence of HCl, food proteins that have not been subjected to denaturation occur. heat treatment, which increases the accessibility of peptide bonds to proteases. Hcl has a bactericidal effect and prevents pathogenic bacteria from entering the intestines. In addition, hydrochloric acid activates pepsinogen and creates an optimal pH for the action of pepsin.

Pepsinogen is a protein consisting of a single polypeptide chain. Under the influence of HCl, it is converted into active pepsin. During the activation process, as a result of partial proteolysis, amino acid residues are cleaved from the N-terminus of the pepsinogen molecule, which contain almost all the positively charged amino acids present in pepsinogen. Thus, negatively charged amino acids are predominant in active pepsin, which are involved in conformational rearrangements of the molecule and the formation of the active center. The active pepsin molecules formed under the influence of HCl quickly activate the remaining pepsinogen molecules (autocatalysis). Pepsin primarily hydrolyzes peptide bonds in proteins formed by aromatic amino acids (phenylalanine, tryptophan, tyrosine). Pepsin is an endopeptidase, therefore, as a result of its action, shorter peptides are formed in the stomach, but not free amino acids.

Infants have an enzyme in their stomach rennin(chymosin), which causes milk to clot. There is no rennin in the stomach of adults; their milk curdles under the influence of HCl and pepsin.

another protease - gastricin. All 3 enzymes (pepsin, rennin and gastrixin) are similar in primary structure

KETOGENIC AND GLYCOGENIC AMINO ACIDS. ANAPLEROTIC REACTIONS, SYNTHESIS OF ESSENTIAL AMINO ACIDS (EXAMPLE).

Amino catabolism is reduced to the formation pyruvate, acetyl-CoA, α -ketoglutarate, succinyl-CoA, fumarate, oxaloacetate glycogenic amino acids- are converted into pyruvate and intermediate products of the TCA cycle and ultimately form oxaloacetate, can be used in the process of gluconeogenesis.

ketogenic amino acids in the process of catabolism are converted into acetoacetate (Lys, Leu) or acetyl-CoA (Leu) and can be used in the synthesis of ketone bodies.

glycoketogenic amino acids are used both for the synthesis of glucose and for the synthesis of ketone bodies, since in the process of their catabolism two products are formed - a certain metabolite of the citrate cycle and acetoacetate (Tri, Fen, Tyr) or acetyl-CoA (Ile).

Anaplerotic reactions - nitrogen-free amino acid residues are used to replenish the amount of metabolites of the general catabolic pathway that is spent on the synthesis of biologically active substances.

The enzyme pyruvate carboxylase (coenzyme - biotin), which catalyzes this reaction, is found in the liver and muscles.

2. Amino acids → Glutamate → α-Ketoglutarate

under the influence of glutamate dehydrogenase or aminotransferases.

3.

Propionyl-CoA, and then succinyl-CoA, can also be formed during the breakdown of higher fatty acids with an odd number of carbon atoms

4. Amino acids → Fumarate

5. Amino acids → Oxaloacetate

Reactions 2, 3 occur in all tissues (except liver and muscles) where pyruvate carboxylase is absent.

VII. BIOSYNTHESIS OF ESSENTIAL AMINO ACIDS

In the human body, the synthesis of eight nonessential amino acids is possible: Ala, Asp, Asn, Ser, Gly, Glu, Gln, Pro. The carbon skeleton of these amino acids is formed from glucose. The α-amino group is introduced into the corresponding α-keto acids as a result of transamination reactions. Universal donor α -amino group serves as glutamate.

Amino acids are synthesized by transamination of α-keto acids formed from glucose

Glutamate also formed during the reductive amination of α-ketoglutarate by glutamate dehydrogenase.

TRANSAMINATION: PROCESS SCHEME, ENZYMES, BIOROLE. BIOROLLE OF ALATE AND ASAT AND CLINICAL SIGNIFICANCE OF THEIR DETERMINATION IN BLOOD SERUM.

Transamination is the reaction of transferring an α-amino group from an amino acid to an α-keto acid, resulting in the formation of a new keto acid and a new amino acid. the transamination process is easily reversible

The reactions are catalyzed by aminotransferase enzymes, the coenzyme of which is pyridoxal phosphate (PP).

Aminotransferases are found both in the cytoplasm and in the mitochondria of eukaryotic cells. More than 10 aminotransferases, differing in substrate specificity, have been found in human cells. Almost all amino acids can undergo transamination reactions. with the exception of lysine, threonine and proline.

• At the first stage, an amino group from the first substrate, aka, is added to the pyridoxal phosphate in the active center of the enzyme using an aldimine bond. An enzyme-pyridoxamine phosphate complex and a keto acid are formed - the first reaction product. This process involves the intermediate formation of 2 Schiff bases.
• In the second stage, the enzyme-pyridoxamine phosphate complex combines with the keto acid and, through the intermediate formation of 2 Schiff bases, transfers the amino group to the keto acid. As a result, the enzyme returns to its native form, and a new amino acid is formed - the second product of the reaction. If the aldehyde group of pyridoxal phosphate is not occupied by the amino group of the substrate, then it forms a Schiff base with the ε-amino group of the lysine radical in the active site of the enzyme

Most often, transamination reactions involve amino acids, the content of which in tissues is significantly higher than others - glutamate, alanine, aspartate and their corresponding keto acids - α -ketoglutarate, pyruvate and oxaloacetate. The main amino group donor is glutamate.

The most abundant enzymes in most mammalian tissues are: ALT (AlAT) catalyzes the transamination reaction between alanine and α-ketoglutarate. This enzyme is localized in the cytosol of cells of many organs, but the largest amount is found in the cells of the liver and heart muscle. ACT catalyzes the transamination reaction between aepartate and α-ketoglutarate. oxaloacetate and glutamate are formed. Its greatest amount is found in the cells of the heart muscle and liver. organ specificity of these enzymes.

Normally, the activity of these enzymes in the blood is 5-40 U/l. When the cells of the corresponding organ are damaged, enzymes are released into the blood, where their activity increases sharply. Since AST and ALT are most active in the cells of the liver, heart and skeletal muscle, they are used to diagnose diseases of these organs. In cardiac muscle cells, the amount of AST significantly exceeds the amount of ALT, and in the liver, the opposite is true. Therefore, simultaneous measurement of the activity of both enzymes in blood serum is especially informative. The ratio of AST/ALT activities is called "de Ritis coefficient". Normally, this coefficient is 1.33±0.42. During myocardial infarction, the activity of AST in the blood increases 8-10 times, and ALT - 2.0 times.

With hepatitis, the activity of ALT in the blood serum increases by ∼8-10 times, and AST - by 2-4 times.

Melanin synthesis.

Types of melanins

Methionine activation reaction

The active form of methionine is S-adenosylmethionine (SAM), a sulfonium form of the amino acid formed by the addition of methionine to the adenosine molecule. Adenosine is formed by the hydrolysis of ATP.

This reaction is catalyzed by the enzyme methionine adenosyltransferase, which is present in all cell types. The structure (-S + -CH 3) in SAM is an unstable grouping that determines high activity methyl group (hence the term "active methionine"). This reaction is unique in biological systems because it appears to be the only known reaction that releases all three phosphate residues of ATP. The cleavage of the methyl group from SAM and its transfer to the acceptor compound is catalyzed by methyltransferase enzymes. SAM is converted to S-adenosylhomocysteine ​​(SAT) during the reaction.

Creatine synthesis

Creatine is necessary for the formation of a high-energy compound in muscles - creatine phosphate. Creatine synthesis occurs in 2 stages with the participation of 3 amino acids: arginine, glycine and methionine. In the kidneys guanidine acetate is formed by the action of glycine amidinotransferase. The guanidine acetate is then transported to the liver where the methylation reaction occurs.

Transmethylation reactions are also used for:

• synthesis of adrenaline from norepinephrine;
• synthesis of anserine from carnosine;
• methylation of nitrogenous bases in nucleotides, etc.;
• inactivation of metabolites (hormones, mediators, etc.) and neutralization of foreign compounds, including drugs.

Inactivation of biogenic amines also occurs:

methylation with the participation of SAM under the action of methyltransferases. In this way, various biogenic amines can be inactivated, but most often gastamine and adrenaline are inactivated. Thus, inactivation of adrenaline occurs by methylation of the hydroxyl group in the ortho position

AMMONIA TOXICITY. ITS FORMATION AND DISHARM.

Catabolism of amino acids in tissues occurs constantly at a rate of ∼100 g/day. In this case, as a result of deamination of amino acids, a large amount of ammonia is released. Significantly smaller quantities are formed during the deamination of biogenic amines and nucleotides. Part of the ammonia is formed in the intestine as a result of the action of bacteria on food proteins (rotting proteins in the intestines) and enters the blood of the portal vein. The concentration of ammonia in the blood of the portal vein is significantly higher than in the general bloodstream. A large amount of ammonia is retained in the liver, which maintains a low level of ammonia in the blood. The normal concentration of ammonia in the blood rarely exceeds 0.4-0.7 mg/l (or 25-40 µmol/l

Ammonia is a toxic compound. Even a slight increase in its concentration has an adverse effect on the body, and primarily on the central nervous system. Thus, an increase in the concentration of ammonia in the brain to 0.6 mmol causes seizures. Symptoms of hyperammonemia include tremors, slurred speech, nausea, vomiting, dizziness, seizures, and loss of consciousness. In severe cases, coma develops with a fatal outcome. The mechanism of the toxic effect of ammonia on the brain and the body as a whole is obviously associated with its effect on several functional systems.

• Ammonia easily penetrates through membranes into cells and in mitochondria shifts the reaction catalyzed by glutamate dehydrogenase towards the formation of glutamate:

α-Ketoglutarate + NADH + H + + NH 3 → Glutamate + NAD + .

A decrease in the concentration of α-ketoglutarate causes:

· inhibition of amino acid metabolism (transamination reaction) and, consequently, the synthesis of neurotransmitters from them (acetylcholine, dopamine, etc.);

· hypoenergetic state as a result of a decrease in the rate of the TCA cycle.

Insufficiency of α-ketoglutarate leads to a decrease in the concentration of metabolites of the TCA cycle, which causes an acceleration of the reaction of oxaloacetate synthesis from pyruvate, accompanied by intensive consumption of CO 2. Increased production and consumption of carbon dioxide during hyperammonemia is especially characteristic of brain cells. An increase in the concentration of ammonia in the blood shifts the pH to the alkaline side (causing alkalosis). This, in turn, increases the affinity of hemoglobin for oxygen, which leads to tissue hypoxia, accumulation of CO 2 and a hypoenergetic state, which mainly affects the brain. High concentrations of ammonia stimulate the synthesis of glutamine from glutamate in nervous tissue (with the participation of glutamine synthetase):

Glutamate + NH 3 + ATP → Glutamine + ADP + H 3 P0 4.

· The accumulation of glutamine in neuroglial cells leads to an increase in osmotic pressure in them, swelling of astrocytes and in high concentrations can cause cerebral edema. A decrease in the concentration of glutamate disrupts the exchange of amino acids and neurotransmitters, in particular the synthesis of γ-aminobutyric acid (GABA), the main inhibitory transmitter. With a lack of GABA and other mediators, the conduction of nerve impulses is disrupted and convulsions occur. The NH 4 + ion practically does not penetrate the cytoplasmic and mitochondrial membranes. An excess of ammonium ion in the blood can disrupt the transmembrane transport of monovalent cations Na + and K +, competing with them for ion channels, which also affects the conduction of nerve impulses.

High intensity processes of deamination of amino acids in tissues and very low level ammonia in the blood indicate that ammonia is actively binding in cells to form non-toxic compounds that are excreted from the body in the urine. These reactions can be considered ammonia neutralization reactions. Several types of such reactions have been found in different tissues and organs. The main reaction of ammonia binding, which occurs in all tissues of the body, is 1.) the synthesis of glutamine under the action of glutamine synthetase:

Glutamine synthetase is localized in cell mitochondria; for the enzyme to function, a cofactor is required - Mg 2+ ions. Glutamine synthetase is one of the main regulatory enzymes of amino acid metabolism and is allosterically inhibited by AMP, glucose-6-phosphate, as well as Gly, Ala and His.

In intestinal cells Under the action of the enzyme glutaminase, the hydrolytic release of amide nitrogen occurs in the form of ammonia:

The glutamate formed in the reaction undergoes transamination with pyruvate. The oc-amino group of glutamic acid is transferred to alanine:

Glutamine is the main donor of nitrogen in the body. The amide nitrogen of glutamine is used for the synthesis of purine and pyrimidine nucleotides, asparagine, amino sugars and other compounds.

METHOD FOR DETERMINING UREA IN BLOOD SERUM

In biological fluids, M. is determined using gasometric methods, direct photometric methods based on the reaction of M. with various substances with the formation of equimolecular quantities of colored products, as well as enzymatic methods using mainly the enzyme urease. Gasometric methods are based on the oxidation of M. with sodium hypobromite in an alkaline environment NH 2 -CO-NH 2 + 3NaBrO → N 2 + CO 2 + 3NaBr + 2H 2 O. The volume of nitrogen gas is measured using a special apparatus, most often the Borodin apparatus. However, this method has low specificity and accuracy. The most common photometric methods are those based on the reaction of metal with diacetyl monooxime (Feron reaction).

To determine urea in blood serum and urine, a unified method is used, based on the reaction of urea with diacetyl monooxime in the presence of thiosemicarbazide and iron salts in an acidic environment. Another unified method for determining M. is the urease method: NH 2 -CO-NH 2 → urease NH 3 +CO 2. The released ammonia forms indophenol with sodium hypochlorite and phenol, which has Blue colour. The color intensity is proportional to the M content in the test sample. The urease reaction is highly specific; only 20 samples are taken for testing. µl blood serum diluted in a ratio of 1:9 with NaCl solution (0.154 M). Sometimes sodium salicylate is used instead of phenol; blood serum is diluted as follows: to 10 µl blood serum add 0.1 ml water or NaCl (0.154 M). The enzymatic reaction in both cases proceeds at 37° for 15 and 3-3 1/2 min respectively.

Derivatives of M., in the molecule of which hydrogen atoms are replaced by acid radicals, are called ureides. Many ureides and some of their halogen-substituted derivatives are used in medicine as medicines. Ureides include, for example, salts of barbituric acid (malonylurea), alloxan (mesoxalyl urea); heterocyclic ureide is uric acid .

GENERAL SCHEME OF HEME DECAY. “DIRECT” AND “INDIRECT” BILIRUBIN, CLINICAL SIGNIFICANCE OF ITS DEFINITION.

Heme (heme oxygenase) - biliverdin (biliverdin reductase) - bilirubin (UDP-glucuranyltransferase) - bilirubin monoglucuronide (UD-glucuronyltransferase) - bilirubin diglucuronide

IN in good condition the concentration of total bilirubin in plasma is 0.3-1 mg/dl (1.7-17 µmol/l), 75% of the total bilirubin is in unconjugated form (indirect bilirubin). In the clinic, conjugated bilirubin is called direct bilirubin because it is water soluble and can quickly react with the diazoreagent to form a compound Pink colour, is a direct Van der Berg reaction. Unconjugated bilirubin is hydrophobic, therefore it is found in the blood plasma in a complex with albumin and does not react with the diazo reagent until it is added organic solvent, such as ethanol, which precipitates albumin. Unconjugated ilirubin, which reacts with the azo dye only after protein precipitation, is called indirect bilirubin.

In patients with hepatocellular pathology, accompanied by a prolonged increase in the concentration of conjugated bilirubin, a third form of plasma bilirubin is found in the blood, in which bilirubin is covalently bound to albumin and therefore cannot be separated in the usual way. In some cases, up to 90% of the total bilirubin content of the blood can be in this form.

METHODS FOR DETECTION OF HEME OF HEMOGLOBIN: PHYSICAL (SPECTRAL ANALYSIS OF HEMOGLOBIN AND ITS DERIVATIVES); PHYSICAL AND CHEMICAL (OBTAINING CRYSTALS OF HEMIN HYDRATE).

Spectral analysis of hemoglobin and its derivatives. The use of spectrographic methods when examining a solution of oxyhemoglobin reveals two systemic absorption bands in the yellow-green part of the spectrum between the Fraunhofer lines D and E; reduced hemoglobin has only one broad band in the same part of the spectrum. Differences in the absorption of radiation by hemoglobin and oxyhemoglobin served as the basis for a method for studying the degree of oxygen saturation of the blood - oxygemometry.

Carbhemoglobin is close in its spectrum to oxyhemoglobin, however, when a reducing substance is added, carbhemoglobin appears two absorption bands. The spectrum of methemoglobin is characterized by one narrow absorption band on the left at the border of the red and yellow parts of the spectrum, a second narrow band at the border of the yellow and green zones, and finally, a third wide band in the green part of the spectrum

Crystals of hemin or hematin hydrochloride. The surface of the stain is scraped onto a glass slide and several grains are crushed. Add 1-2 grains to them table salt and 2-3 drops of ice-cold vinegar. Cover everything with a cover slip and heat it carefully, without bringing it to a boil. The presence of blood is proven by the appearance of brown-yellow microcrystals in the form of rhombic tablets. If the crystals are poorly formed, they have the appearance of a hemp seed. Obtaining hemin crystals certainly proves the presence of blood in the test object. A negative test result is irrelevant. Fat and rust make it difficult to obtain hemin crystals

REACTIVE SPECIES OF OXYGEN: SUPEROXIDE ANION, HYDROGEN PEROXIDE, HYDROXYL RADICAL, PEROXYNITRITE. THEIR FORMATION, CAUSES OF TOXICITY. PHYSIOLOGICAL ROLE OF ROS.

In the CPE, about 90% of the O2 entering the cells is absorbed. The rest of O 2 is used in other ORPs. Enzymes involved in ORR using O2 are divided into 2 groups: oxidases and oxygenases.

Oxidases use molecular oxygen only as an electron acceptor, reducing it to H 2 O or H 2 O 2.

Oxygenases include one (monooxygenase) or two (dioxygenase) oxygen atoms in the resulting reaction product.

Although these reactions are not accompanied by the synthesis of ATP, they are necessary for many specific reactions in the metabolism of amino acids), the synthesis of bile acids and steroids), and in the reactions of neutralization of foreign substances in the liver

In most reactions involving molecular oxygen, its reduction occurs in stages, with the transfer of one electron at each stage. During single-electron transfer, the formation of intermediate high-resolution active forms oxygen.

In an unexcited state, oxygen is non-toxic. The formation of toxic forms of oxygen is associated with the characteristics of its molecular structure. O 2 contains 2 unpaired electrons, which are located in different orbitals. Each of these orbitals can accept one more electron.

Complete reduction of O2 occurs as a result of 4 one-electron transitions:

Superoxide, peroxide and hydroxyl radical are active oxidizing agents, which pose a serious danger to many structural components of the cell.

Reactive oxygen species can strip electrons from many compounds, turning them into new free radicals, initiating oxidative chain reactions

The damaging effect of free radicals on cell components. 1 - destruction of proteins; 2 - ER damage; 3 - destruction of the nuclear membrane and DNA damage; 4 - destruction of mitochondrial membranes; penetration of water and ions into the cell.

Formation of superoxide in CPE."Leakage" of electrons into the CPE can occur during electron transfer with the participation of coenzyme Q. Upon reduction, ubiquinone is converted into the semiquinone radical anion. This radical reacts non-enzymatically with O2 to form a superoxide radical.

Most of the reactive oxygen species are formed during the transfer of electrons to the CPE, primarily during the functioning of the QH 2 dehydrogenase complex. This occurs as a result of non-enzymatic transfer ("leakage") of electrons from QH 2 to oxygen (

at the stage of electron transfer with the participation of cytochrome oxidase (complex IV), “leakage” of electrons does not occur due to the presence in the enzyme of special active centers containing Fe and Cu and reducing O 2 without releasing intermediate free radicals.

In phagocytic leukocytes, during the process of phagocytosis, the absorption of oxygen and the formation of active radicals increase. Reactive oxygen species are formed as a result of the activation of NADPH oxidase, predominantly localized on the outer side of the plasma membrane, initiating the so-called “respiratory burst” with the formation of reactive oxygen species

The body’s protection from the toxic effects of reactive oxygen species is associated with the presence of highly specific enzymes in all cells: superoxide dismutase, catalase, glutathione peroxidase, as well as with the action of antioxidants.

DISPOSAL OF REACTIVE OXYGEN SPECIES. ENZYMIC ANTIOXIDANT SYSTEM (CATALASE, SUPEROXIDE DISMUTASE, GLUTATHIONE PEROXIDASE, GLUTATHIONE REDUCTASE). PROCESS DIAGRAMS, BIOROLLE, PLACE OF PROCESS.

Superoxide dismutase catalyzes the dismutation reaction of superoxide anion radicals:
O2.- + O2.- = O2 + H 2O2
During the reaction, hydrogen peroxide was formed, it is capable of inactivating SOD, therefore superoxide dismutase always “works” in pairs with scalase, which quickly and efficiently breaks down hydrogen peroxide into absolutely neutral compounds.

Catalase (KF 1.11.1.6)– hemoprotein, which catalyzes the reaction of neutralization of hydrogen peroxide formed as a result of the dismutation reaction of the superoxide radical:
2H2O2 = 2H2O + O2

Glutathione peroxide catalyzes reactions in which the enzyme reduces hydrogen peroxide to water, as well as the reduction of organic hydroperoxides (ROOH) to hydroxy derivatives, and as a result converts to the oxidized disulfide form GS-SG:
2GSH + H2O2 = GS-SG + H2O
2GSH + ROOH = GS-SG + ROH +H2O

Glutathione peroxidase neutralizes not only H2O2, but also various organic lipid peroxyls that are formed in the body when LPO is activated.

Glutathione reductase (KF 1.8.1.7)– flavoprotein with a prosthetic group flavin adenine dinucleotide, consists of two identical subunits. Glutathione reductase catalyzes the reaction of glutathione reduction from its oxidized form GS-SG, and all other glutathione synthetase enzymes use it:
2NADPH + GS-SG = 2NADP + 2 GSH

This is a classic cytosolic enzyme of all eukaryotes. Glutathione transferase catalyzes the reaction:
RX + GSH = HX + GS-SG

CONJUGATION PHASE IN THE SYSTEM FOR DISPOSAL OF TOXIC SUBSTANCES. TYPES OF CONJUGATION (EXAMPLES OF REACTIONS WITH FAPS, UDFGK)

Conjugation is the second phase of neutralization of substances, during which other molecules or groups of endogenous origin are added to the functional groups formed in the first stage, increasing hydrophilicity and reducing the toxicity of xenobiotics

1. Participation of transferases in conjugation reactions

UDP-glucuronyl transferase. Uridine diphosphate (UDP)-glucuronyltransferases, located mainly in the ER, add a glucuronic acid residue to a molecule of a substance formed during microsomal oxidation

IN general view: ROH + UDP-C6H9O6 = RO-C6H9O6 + UDP.

Sulfotransferases. Cytoplasmic sulfotransferases catalyze the conjugation reaction, during which the sulfuric acid residue (-SO3H) from 3"-phosphoadenosine-5"-phosphosulfate (FAPS) is added to phenols, alcohols or amino acids

The general reaction is: ROH + FAF-SO3H = RO-SO3H + FAF.

The enzymes sulfotransferase and UDP-glucuronyltransferase are involved in the neutralization of xenobiotics, inactivation of drugs and endogenous biologically active compounds.

Glutathione transferases. Special place Glutathione transferases (GT) are among the enzymes involved in the neutralization of xenobiotics, inactivation of normal metabolites, and drugs. Glutathione transferases function in all tissues and play an important role in the inactivation of their own metabolites: some steroid hormones, bilirubin, bile acids. In the cell, GTs are mainly localized in the cytosol, but there are enzyme variants in the nucleus and mitochondria.

Glutathione is a tripeptide Glu-Cys-Gly (the glutamic acid residue is attached to cys-teine ​​by the carboxyl group of the radical). GTs have broad specificity for substrates, the total number of which exceeds 3000. GTs bind many hydrophobic substances and inactivate them, but only those that have a polar group undergo chemical modification with the participation of glugathione. That is, substrates are substances that, on the one hand, have an electrophilic center (for example, an OH group), and on the other hand, hydrophobic zones. Neutralization, i.e. chemical modification of xenobiotics with the participation of GT can be carried out by three different ways:

by conjugation of the substrate R with glutathione (GSH): R + GSH → GSRH,

as a result of nucleophilic substitution: RX + GSH → GSR + HX,

reduction of organic peroxides to alcohols: R-HC-O-OH + 2 GSH → R-HC-OH + GSSG + H2O

In the reaction: UN - hydroperoxide group, GSSG - oxidized glutathione.

The neutralization system with the participation of GT and glutathione plays a unique role in the formation of the body’s resistance to a wide variety of influences and is the most important protective mechanism of the cell. During the biotransformation of some xenobiotics under the influence of HT, thioesters (RSG conjugates) are formed, which are then converted into mercaptans, among which toxic products are found. But GSH conjugates with most xenobiotics are less reactive and more hydrophilic than the original substances, and therefore less toxic and easier to remove from the body

GTs, with their hydrophobic centers, can non-covalently bind a huge number of lipophilic compounds (physical neutralization), preventing their penetration into the lipid layer of membranes and disruption of cell functions. Therefore, GT is sometimes called intracellular albumin.

GTs can covalently bind xenobiotics, which are strong electrolytes. The addition of such substances is “suicide” for GT, but additional defense mechanism for the cell.

Acetyltransferases, methyltransferases

Acetyltransferases catalyze conjugation reactions - the transfer of an acetyl residue from acetyl-CoA to the nitrogen group -SO2NH2, for example in the composition of sulfonamides. Membrane and cytoplasmic methyltransferases with the participation of SAM methylate the -P=O, -NH2 and SH groups of xenobiotics.

The role of epoxide hydrolases in the formation of diols

Some other enzymes also take part in the second phase of neutralization (conjugation reaction). Epoxide hydrolase (epoxide hydratase) adds water to the epoxides of benzene, benzopyrene and other polycyclic hydrocarbons formed during the first phase of neutralization and converts them into diols (Fig. 12-8). Epoxides formed during microsomal oxidation are carcinogens. They have high chemical activity and can participate in non-enzymatic alkylation reactions of DNA, RNA, and proteins. Chemical modifications of these molecules can lead to the degeneration of a normal cell into a tumor cell.

ROLE OF PROTEIN IN NUTRITION, NORMS, NITROGEN BALANCE, WEAR RATIO, PHYSIOLOGICAL PROTEIN MINIMUM. PROTEIN INSUFFICIENCY.

AA contain almost 95% of all nitrogen, so they maintain the nitrogen balance of the body. Nitrogen balance- the difference between the amount of nitrogen taken in from food and the amount of nitrogen excreted. If the amount of nitrogen supplied is equal to the amount released, then nitrogen balance. This condition occurs in a healthy person with normal nutrition. The nitrogen balance can be positive (more nitrogen enters than is excreted) in children and patients. Negative nitrogen balance (nitrogen excretion prevails over its intake) is observed during aging, fasting and during serious illnesses. With a protein-free diet, the nitrogen balance becomes negative. The minimum amount of protein in food required to maintain nitrogen balance is 30-50 g/cyt, while the optimal amount for average physical activity is ∼100-120 g/day.

amino acids, the synthesis of which is complex and uneconomical for the body, are obviously more profitable to obtain from food. Such amino acids are called essential. These include phenylalanine, methionine, threonine, tryptophan, valine, lysine, leucine, isoleucine.

Two amino acids - arginine and histidine are called partially replaceable. - tyrosine and cysteine ​​are conditionally replaceable, since their synthesis requires essential amino acids. Tyrosine is synthesized from phenylalanine, and the formation of cysteine ​​requires the sulfur atom of methionine.

The remaining amino acids are easily synthesized in cells and are called non-essential. These include glycine, aspartic acid, asparagine, glutamic acid, glutamine, series, pro