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 excreted from the body. There are three types of nitrogen balance: nitrogen balance, positive nitrogen balance, negative nitrogen balance.
At positive nitrogen balance the intake of nitrogen prevails over its release. Under physiological conditions, a true positive nitrogen balance occurs (pregnancy, lactation, childhood). For children at the age of 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 there is a delay in the body of the end products of nitrogen metabolism.
At negative nitrogen balance nitrogen excretion prevails over its intake. This condition is possible with diseases such as tuberculosis, rheumatism, cancer. Nitrogen balance characteristic of healthy adults, in which the intake of nitrogen is equal to its excretion.
Nitrogen metabolism is characterized wear rate, which is understood as the amount of protein that is lost from the body in conditions of complete protein starvation. For an adult, it is 53 mg / kg (or 24 g / day). In newborns, the wear factor is higher and amounts to 120 mg/kg. Nitrogen balance is provided by protein nutrition.
Protein diet characterized by certain quantitative and qualitative criteria.
Quantitative criteria for protein nutrition
Protein minimum- the amount of protein that provides nitrogen balance, provided that all energy costs are provided by carbohydrates and fats. It is 40-45 g / day. With prolonged use of the 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 reviewed in the direction of 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
More valuable proteins for 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
- digest well in gastrointestinal tract
Proteins of animal origin meet these requirements to a greater extent. For newborns, all proteins should be complete (breast milk proteins). At the age of 3-4 years, about 70-75% should be complete proteins. For adults, their share should be about 50%.
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.
See what the "Physiological minimum of protein" is in other dictionaries:
See Nitrogen Low... Big Medical Dictionary
Big Medical Dictionary
- (syn. physiological minimum of protein) the smallest amount of protein introduced with food, at which nitrogen balance is maintained ... Medical Encyclopedia
OBLITERATION- (lat. obliteratio destruction), a term used to denote the closure, destruction of a particular cavity or lumen through the growth of tissue coming from the side of the walls of this cavity formation. The indicated growth is more often ... ...
General view of a tree in the Old Botanical Garden of Marburg (... Wikipedia
This term has other meanings, see Aging. Old woman. Ann Powder on April 8, 1917, her 110th birthday. Wrinkled and dry skin is a typical sign of human aging ... Wikipedia
This term has other meanings, see Aging. Human aging, like the aging of other organisms, is a biological process of gradual degradation of parts and systems of the human body and the consequences of this process. Whereas ... ... Wikipedia
MENINGITIS- - inflammation of the membranes of the brain and spinal cord, usually of infectious origin. Meningitis is classified according to etiology (bacterial, viral, fungal, etc.), the nature of the inflammatory process (purulent, serous), the course (acute, ... ... Encyclopedic Dictionary of Psychology and Pedagogy
BIRTH- BIRTH. Contents: I. Definition of the concept. Changes in the body during R. Causes of the onset of R ............................ 109 II. Clinical current of physiological R. . 132 Sh. Mechanics R. ................. 152 IV. Leading P .............. 169 V ... Big Medical Encyclopedia
This article should be wikified. Please, format it according to the rules for formatting articles. Multiple sclerosis ... Wikipedia
The protein minimum is the minimum amount of protein that allows you to maintain nitrogen balance in the body (nitrogen is a very important element for all living beings, since it is part of all amino acids and proteins). It has been established that during fasting for 8-10 days, a constant amount of protein is broken down in the body - approximately 23.2 grams (for a person weighing 70 kg). However, this does not mean at all that the intake of the same amount of protein with food will fully satisfy the needs of our body for this nutritional component, especially when playing sports. The protein minimum is only able to maintain the basic physiological processes at the proper level, and even then for a very short time.
The protein optimum is the amount of protein in food that fully satisfies a person’s needs for nitrogenous compounds and thus provides the necessary components for muscles recovering after exercise, maintains the body’s high performance, and contributes to the formation of a sufficient level of resistance to infectious diseases. The protein optimum for an adult woman's body is approximately 90 - 100 grams of protein per day, and with regular intensive sports, this can significantly increase - up to 130 - 140 grams per day and even more. It is believed that in order to fulfill the protein optimum per day when performing physical exercises, for every kilogram of body weight, an average intake of 1.5 grams of protein and more is required. However, even with the most intense training regimens in sports, the amount of protein should not exceed 2 - 2.5 grams per kilogram of body weight. If you attend sports sections or fitness clubs with a purely recreational purpose, then the optimal protein content in your diet should be considered such an amount that ensures the intake of 1.5 - 1.7 grams of protein per kilogram of body weight.
However, compliance with the protein minimum and protein optimum during sports is not the only condition for good nutrition, which ensures recovery processes in the body after active training. The fact is that food proteins can differ significantly in their nutritional value. For example, proteins of animal origin are optimal for the human body in terms of their amino acid composition. They contain all the essential amino acids necessary for the growth and rapid recovery of muscle tissue during sports. Proteins contained in plant foods contain very small amounts of some essential amino acids or are characterized by the complete absence of some of them. Therefore, when playing sports, the diet will be optimal, which necessarily includes meat and dairy products, eggs and fish.
Lecture No. 1. Digestion of proteins in the gastrointestinal tract. nitrogen balance. Dietary protein standards.
Lecture plan:
1. The biological role of proteins.
2. Nitrogen balance and its forms.
3. Norms of protein in nutrition (wear coefficient, protein minimum and protein optimum). Criteria for the usefulness of food protein.
4. Digestion of proteins in the gastrointestinal tract. Characterization of enzymes of gastric, pancreatic and intestinal juice. The role of hydrochloric acid in protein digestion. The mechanism of activation of proteolytic enzymes.
5. Gastrointestinal hormones (structure, biological role).
6. Processes of putrefaction of proteins in the large intestine. Neutralization of toxic products of protein decay. Indican formation. The reaction for the determination of indican in urine, KDZ.
The biological role of proteins.
Proteins perform the following functions: plastic (structural), catalytic, protective, transport, regulatory, energy.
Nitrogen balance and its forms.
Nitrogen balance (AB) is the difference between the total nitrogen that enters the body with food and the total nitrogen that is excreted from the body with urine. Forms of A.B.: 1) nitrogen balance (N food = N urine + feces); 2) positive nitrogen balance (N food ˃ N urine + feces); 3) negative A.B. (N food ˂ N urine+feces).
Protein norms in nutrition (wear and tear coefficient, protein minimum and protein optimum). Criteria for the usefulness of food protein.
Proteins are made up of 20 proteinogenic amino acids.
Essential amino acids - cannot be synthesized in human tissues and must be ingested daily with food. These include: valine, leucine, isoleucine, methionine, threonine, lysine, tryptophan, phenylalanine.
Partially essential amino acids (arginine and histidine) can be synthesized in the human body, but do not cover daily requirement, especially in childhood.
Non-essential amino acids can be synthesized in the human body from metabolic intermediates.
Criteria for the usefulness of a food protein: 1) biological value is the amino acid composition and the ratio of individual amino acids; 2) protein digestibility in the gastrointestinal tract.
A complete protein contains all essential amino acids in optimal proportions and is easily hydrolyzed by gastrointestinal enzymes. Egg and milk proteins have the greatest biological value. They are also easily digestible. Of vegetable proteins, soy proteins occupy the first place.
The wear factor is the amount of endogenous protein that breaks down daily to final products. The average is 3.7 g of nitrogen / day, or 23 g of protein / day.
The physiological protein minimum is the amount of protein in food that allows you to maintain nitrogen balance at rest. For an adult healthy person - 40-50 g / day.
The protein optimum is the amount of protein in food that supports a full life. For a healthy adult - 80-100 g / day (1.5 g per kg of body weight).
Digestion of proteins in the gastrointestinal tract. Characterization of enzymes of gastric, pancreatic and intestinal juice. The role of hydrochloric acid in protein digestion. The mechanism of activation of proteolytic enzymes.
The breakdown of proteins in the gastrointestinal tract is hydrolytic. The enzymes are called proteases or peptidases. The process of protein hydrolysis is called proteolysis. Gastrointestinal peptidases are divided into 2 groups:
1) endopeptidases - catalyze the hydrolysis of internal peptide bonds; these include enzymes: pepsin (gastric juice), trypsin and chymotrypsin (pancreatic juice):
2) exopeptidases - catalyze the hydrolysis of terminal peptide bonds; these include enzymes: carboxypeptidase (pancreatic juice), aminopeptidases, tri- and dipeptidases (intestinal juice).
Proteolytic Enzymes are synthesized and secreted into the intestinal lumen in the form of proenzymes - inactive forms. Activation occurs by limited proteolysis - cleavage of the inhibitor peptide. Hydrolysis of proteins in fatty acids: protein → peptides → amino acids proceeds gradually.
The role of hydrochloric acid: activates pepsin, creates acidity (1.5-2), denatures proteins, has a bactericidal effect.
The absorption of free amino acids into the blood proceeds by active transport with the participation of specialized carrier proteins.
nitrogen balance nitrogen balance.
The remaining amino acids are easily synthesized in cells and are called nonessential. These include glycine, aspartic acid, asparagine, glutamic acid, glutamine, series, proline, alanine.
However, protein-free nutrition ends with the death of the body. The exclusion of even one essential amino acid from the diet leads to incomplete assimilation of other amino acids and is accompanied by the development of a negative nitrogen balance, exhaustion, stunting and dysfunction of the nervous system.
With a protein-free diet, 4g of nitrogen is released per day, which is 25g of protein (WEAR FACTOR-T).
Physiological protein minimum - the minimum amount of protein in food necessary to maintain nitrogen balance - 30-50 g / day.
PROTEIN DIGESTION IN THE GIT. CHARACTERISTICS OF GASTRIC PEPTIDASES, FORMATION AND ROLE OF HYDROchlorIC ACID.
The content of free amino acids in foods 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 the peptide bonds formed by certain amino acids with the highest speed. Proteases that hydrolyze peptide bonds within 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 action of all proteases of the gastrointestinal tract, food proteins break down into individual amino acids, which then enter the tissue cells.
Formation and role of hydrochloric acid
The main digestive function of the stomach is that the digestion of protein begins in it. Hydrochloric acid plays an important role in this process. Proteins entering the stomach stimulate the excretion histamine and groups of protein hormones - gastrins, which, in turn, cause the secretion of HCI and proenzyme - pepsinogen. HCI is produced in the parietal cells of the stomach
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
The dissociation of H 2 CO 3 leads to the formation of bicarbonate, which, with the participation of special proteins, is released into the plasma. Ions C1 - enter the lumen of the stomach through the chloride channel.
The pH is reduced to 1.0-2.0.
Under the action of HCl, denaturation of food proteins that have not undergone heat treatment occurs, which increases the availability of peptide bonds for proteases. HCl has a bactericidal effect and prevents pathogenic bacteria from entering the intestine. In addition, hydrochloric acid activates pepsinogen and creates an optimum pH for the action of pepsin.
Pepsinogen is a protein consisting of a single polypeptide chain. Under the action of HCl, it is converted into active pepsin. In the process of activation, as a result of partial proteolysis, amino acid residues are cleaved from the N-terminus of the pepsinogen molecule, which contain almost all positively charged amino acids present in pepsinogen. Thus, negatively charged amino acids, which are involved in the conformational rearrangements of the molecule and the formation of the active center, are predominant in active pepsin. The active pepsin molecules formed under the action 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.
In infants, the stomach contains an enzyme rennin(chymosin), which causes milk to clot. There is no rennin in the stomach of adults; their milk is curdled under the action of HCl and pepsin.
another protease gastrixin. All 3 enzymes (pepsin, rennin and gastrixin) are similar in primary structure
KETOGENIC AND GLYCOGENIC AMINO ACIDS. ANAPLEROTIC REACTIONS, SYNTHESIS OF FUNCTIONAL AMINO ACIDS (EXAMPLE).
The catabolism of amino-t is reduced to the formation pyruvate, acetyl-CoA, α -ketoglutarate, succinyl-CoA, fumarate, oxaloacetate glycogenic amino acids- are converted into pyruvate and TCA intermediates and ultimately form oxaloacetate, can be used in the process of gluconeogenesis.
ketogenic aminok-you in the process of catabolism are converted into acetoacetate (Liz, 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 2 products are formed - a certain metabolite of the citrate cycle and acetoacetate (Tri, Phen, Tyr) or acetyl-CoA (Ile).
Anaplerotic reactions - nitrogen-free amino acid residues are used to replenish the amount of metabolites of the common catabolism 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
by the action 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 non-essential amino acids is possible: Ala, Asp, Asn, Ser, Gli, 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.
By transamination of α-keto acids formed from glucose, amino acids are synthesized
Glutamate also formed by reductive amination of α-ketoglutarate by glutamate dehydrogenase.
TRANSAMINATION: PROCESS SCHEME, ENZYMES, BIOROL. BIOROL ALAT AND ASAT AND CLINICAL SIGNIFICANCE OF THEIR DETERMINATION IN BLOOD SERUM.
Transamination is the reaction of transferring an α-amino group from ak-s to α-keto acid, resulting in the formation of a new keto acid and a new ak. 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 have been found in human cells, differing in substrate specificity. Almost all amino acids can enter into transamination reactions, with the exception of lysine, threonine and proline.
- At the first stage, an amino group from the first substrate, ak-s, is attached to 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 product of the reaction. This process involves the intermediate formation of 2 Schiff bases.
- At 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 center of the enzyme
Most often, amino acids are involved in transamination reactions, the content of which in tissues is much higher than the rest - glutamate, alanine, aspartate and their corresponding keto acids - α -ketoglutarate, pyruvate and oxaloacetate. The main donor of the amino group is glutamate.
The most common 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 the cells of many organs, but its greatest amount is found in the cells of the liver and heart muscle. ACT (AST) 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. the organ specificity of these enzymes.
Normally, the activity of these enzymes in the blood is 5-40 U/L. If the cells of the corresponding organ are damaged, the enzymes are released into the blood, where their activity increases sharply. Since ACT 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 the cells of the heart muscle, the amount of ACT significantly exceeds the amount of ALT, and vice versa in the liver. Therefore, the simultaneous measurement of the activity of both enzymes in blood serum is especially informative. The ratio of ACT/ALT activities is called "de Ritis coefficient". Normally, this coefficient is 1.33±0.42. In myocardial infarction, ACT activity in the blood increases 8-10 times, and ALT - 2.0 times.
In hepatitis, the activity of ALT in the blood serum increases by ∼8-10 times, and ACT - by 2-4 times.
Synthesis of melanins.
Types of melanins
Methionine activation reaction
The active form of methionine is S-adenosylmethionine (SAM) - the sulfonium form of the amino acid, which is formed as a result of the addition of methionine to the adenosine molecule. Adenosine is formed from 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 group that determines the high activity of the 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 ATP phosphate residues. 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 the muscles - creatine phosphate. The synthesis of creatine occurs in 2 stages with the participation of 3 amino acids: arginine, glycine and methionine. in the kidneys guanidinoacetate is formed by the action of glycinamidinotransferase. The guanidine acetate is then transported into the liver where the methylation reaction takes place.
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 involving SAM by methyltransferases. In this way, various biogenic amines can be inactivated, but most often, gastamine and adrenaline are inactivated. So, the inactivation of adrenaline occurs by methylation of the hydroxyl group in the ortho position
AMMONIA TOXICITY. ITS FORMATION AND NEUTRALIZATION.
Catabolism of amino acids in tissues occurs constantly at a rate of ∼100 g/day. At the same time, as a result of deamination of amino acids, a large amount of ammonia is released. Much smaller quantities it is 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 of proteins in the intestine) 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 circulation. A large amount of ammonia is retained in the liver, which maintains a low content of it in the blood. The concentration of ammonia in the blood normally 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 above all on the central nervous system. Thus, an increase in the concentration of ammonia in the brain to 0.6 mmol causes convulsions. Symptoms of hyperammonemia include tremor, slurred speech, nausea, vomiting, dizziness, seizures, loss of consciousness. In severe cases, a 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 glugamate:
α-Ketoglutarate + NADH + H + + NH 3 → Glutamate + NAD +.
A decrease in the concentration of α-ketoglutarate causes:
Inhibition of amino acid metabolism (transamination reactions) and, consequently, the synthesis of neurotransmitters from them (acetylcholine, dopamine, etc.);
hypoenergetic state as a result of a decrease in the speed of the TCA.
Deficiency of α-ketoglutarate leads to a decrease in the concentration of TCA metabolites, which causes an acceleration of the reaction for the synthesis of oxaloacetate from pyruvate, accompanied by intensive consumption of CO 2 . Increased formation and consumption of carbon dioxide in hyperammonemia is especially characteristic of brain cells. An increase in the concentration of ammonia in the blood shifts the pH to the alkaline side (causes alkalosis). This, in turn, increases the affinity of hemoglobin for oxygen, which leads to tissue hypoxia, accumulation of CO 2 and a hypoenergetic state, from which the brain mainly suffers. High concentrations of ammonia stimulate the synthesis of glutamine from glutamate in the nervous tissue (with the participation of glutamine synthetase):
Glutamate + NH 3 + ATP → Glutamine + ADP + H 3 P0 4.
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 glutamate concentration disrupts the metabolism of amino acids and neurotransmitters, in particular the synthesis of y-aminobutyric acid (GABA), the main inhibitory mediator. With a lack of GABA and other mediators, the conduction is disrupted nerve impulse, convulsions occur. The NH 4 + ion practically does not penetrate through the cytoplasmic and mitochondrial membranes. An excess of ammonium ion in the blood can disrupt the transmembrane transfer of monovalent Na + and K + cations, competing with them for ion channels, which also affects the conduction of nerve impulses.
The high intensity of amino acid deamination processes in the tissues and the very low level of ammonia in the blood indicate that the cells actively bind ammonia to form non-toxic compounds that are excreted from the body with urine. These reactions can be considered ammonia neutralization reactions. Several types of such reactions have been found in different tissues and organs. The main ammonia binding reaction occurring in all tissues of the body is 1.) the synthesis of glutamine under the action of glutamine synthetase:
Glutamine synthetase is localized in the mitochondria of cells; for the enzyme to work, a cofactor is needed - 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 in the form of ammonia occurs:
The glutamate formed in the reaction undergoes transamination with pyruvate. os-Amino group of glutamic acid is transferred to alanine:
Glutamine is the main donor of nitrogen in the body. Amide nitrogen of glutamine is used for the synthesis of purine and pyrimidine nucleotides, asparagine, amino sugars and other compounds.
METHOD FOR THE DETERMINATION OF 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 amounts of colored products, as well as enzymatic methods using mainly the urease enzyme. Gasometric methods are based on the oxidation of M. with sodium hypobromite in an alkaline medium NH 2 -CO-NH 2 + 3NaBrO → N 2 + CO 2 + 3NaBr + 2H 2 O. The volume of gaseous nitrogen is measured using a special apparatus, most often Borodin's apparatus. However, this method has low specificity and accuracy. Of the photometric methods, the most common are those based on M.'s reaction with diacetyl monooxime (Feron's reaction).
To determine urea in blood serum and urine, a unified method is used, based on the reaction of M. with diacetyl monooxime in the presence of thiosemicarbazide and iron salts in an acidic medium. Another unified method for determining M. is the urease method: NH 2 -CO-NH 2 → NH 3 +CO 2 urease. The released ammonia forms with sodium hypochlorite and phenol indophenol, which has a blue color. The color intensity is proportional to M.'s content in the test sample. The urease reaction is highly specific, only 20 µl blood serum diluted 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 NaCI (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 the hydrogen atoms are replaced by acid radicals, are called ureides. Many ureides and some of their halogenated derivatives are used in medicine as medicines. Ureides include, for example, salts of barbituric acid (malonylurea), alloxan (mesoxalylurea); uric acid is a heterocyclic ureide .
GENERAL SCHEME OF HEME DECAY. "DIRECT" AND "INDIRECT" BILIRUBIN, CLINICAL SIGNIFICANCE OF ITS DETERMINATION.
Heme (hemoxygenase) -biliverdin (biliverdin reductase) - bilirubin (UDP-glucuranyl transferase) - bilirubin monoglucuronide (UD-glucuronyl transferase) - bilirubin diglucuronide
In the normal state, 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 because it is water-soluble and can quickly interact with a diazo reagent, forming a pink compound - this is a direct Van der Berg reaction. Unconjugated bilirubin is hydrophobic, therefore it is contained in the blood plasma in a complex with albumin and does not react with a diazo reagent until an organic solvent, such as ethanol, is added, which precipitates albumin. Unconjugated ilirubin that 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 it cannot be separated in the usual way. In some cases, up to 90% of the total blood bilirubin may be in this form.
METHODS FOR DETECTING HEMOGLOBIN HEME: PHYSICAL (SPECTRAL ANALYSIS OF HEMOGLOBIN AND ITS DERIVATIVES); PHYSICAL AND CHEMICAL (OBTAINING CRYSTALS OF HEMIN HYDROHYDRATE).
Spectral analysis of hemoglobin and its derivatives. The use of spectrographic methods when considering a solution of oxyhemoglobin reveals two systemic absorption bands in the yellow-green part of the spectrum between the Fraunhofer lines D and E, while reduced hemoglobin has only one wide band in the same part of the spectrum. Differences in the absorption of radiation by hemoglobin and oxyhemoglobin formed the basis for a method for studying the degree of blood oxygen saturation - oximetry.
Carbhemoglobin is close in its spectrum to oxyhemoglobin, however, when a reducing agent is added, two absorption bands appear in carbhemoglobin. 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. From the surface of the stain, it is scraped off onto a glass slide and several grains are crushed. To them are added 1-2 grains of table salt and 2-3 drops of glacial acetic acid. Everything is covered with a coverslip and carefully, without boiling, heat up. The presence of blood is proved by the appearance of brown-yellow microcrystals in the form of rhombic plates. If the crystals are poorly formed, they look like hemp seeds. Obtaining hemin crystals certainly proves the presence of blood in the test object. A negative test result is irrelevant. Admixture of fat, rust make it difficult to obtain hemin crystals
ACTIVE OXYGEN SPECIES: SUPEROXIDE ANION, HYDROGEN PEROXIDE, HYDROXY RADICAL, PEROXYNITRITE. THEIR FORMATION, CAUSES OF TOXICITY. PHYSIOLOGICAL ROLE OF ROS.
About 90% of O 2 entering the cells is absorbed in the CPE. The rest of the O 2 is used in other OVRs. Enzymes involved in OVR 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 (monooxygenases) or two (dioxygenases) oxygen atoms in the resulting reaction product.
Although these reactions are not accompanied by ATP synthesis, they are necessary for many specific reactions in amino acid metabolism), synthesis bile acids and steroids), 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. With one-electron transfer, the formation of intermediate highly reactive oxygen species occurs.
In an unexcited state, oxygen is non-toxic. The formation of toxic forms of oxygen is associated with the peculiarities 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 O 2 occurs as a result of 4 one-electron transitions:
Superoxide, peroxide and hydroxyl radical are active oxidizing agents, which poses a serious danger to many structural components cells
Reactive oxygen species can split off electrons from many compounds, converting 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. The "leakage" of electrons in 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 interacts non-enzymatically with O 2 to form a superoxide radical. 
Most reactive oxygen species are formed during the transfer of electrons in 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), there is no "leakage" of electrons 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, in the process of phagocytosis, oxygen uptake 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
Protection of the body from the toxic effects of reactive oxygen species is associated with the presence in all cells of highly specific enzymes: superoxide dismutase, catalase, glutathione peroxidase, as well as with the action of antioxidants.
NEUTRALIZATION OF ACTIVE OXYGEN FORMS. ENZYMATIC ANTIOXIDANT SYSTEM (CATALASE, SUPEROXIDE DISMUTHASE, GLUTATHIONE PEROXIDASE, GLUTATHIONE REDUCTASE). SCHEMES OF PROCESSES, BIOROL, PLACE OF PROCESS.
Superoxide dismutase catalyzes the dismutation reaction of superoxide anion-radicals:
O2.- + O2.- \u003d O2 + H 2O2
During the reaction, hydrogen peroxide was formed, it is able to inactivate SOD, therefore superoxide dismutase always “works” in pair with scatalase, which quickly and efficiently breaks down hydrogen peroxide into absolutely neutral compounds.
Catalase (CF 1.11.1.6)- hemoprotein, which catalyzes the reaction of neutralization of hydrogen peroxide, which is formed as a result of the dismutation reaction of the superoxide radical:
2H2O2 = 2H2O + O2
Glutathione peroxide catalyzes the 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 passes into 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, which are formed in the body during the activation of LPO.
Glutathione reductase (CF 1.8.1.7)- flavoprotein with the prosthetic group flavin adenine dinucleotide, consists of two identical subunits. Glutathione reductase catalyzes the reduction reaction of glutathione from its oxidized form GS-SG, and all other glutathione synthetase enzymes use it:
2NADPH + GS-SG = 2NADP + 2GSH
This is a classic cytosolic enzyme of all eukaryotes. Glutathione transferase catalyzes the reaction:
RX+GSH=HX+GS-SG
PHASE OF CONJUGATION IN THE SYSTEM OF NEUTRALIZATION OF TOXIC SUBSTANCES. TYPES OF CONJUGATION (EXAMPLES OF REACTIONS WITH FAPS, UDFGK)
Conjugation - the second phase of the neutralization of substances, during which the functional groups formed at the first stage are attached to other molecules or groups of endogenous origin, which increase the hydrophilicity and reduce the toxicity of xenobiotics
1. Participation of transferases in conjugation reactions
UDP-glucuronyltransferase. Uridine diphosphate (UDP)-glucuronyltransferases localized mainly in the ER attach a glucuronic acid residue to a molecule of a substance formed during microsomal oxidation
In general: 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 attached to phenols, alcohols or amino acids
Reaction in general form: ROH + FAF-SO3H = RO-SO3H + FAF.
Enzymes sulfotransferase and UDP-glucuronyltransferase are involved in the neutralization of xenobiotics, inactivation of drugs and endogenous biologically active compounds.
Glutathione transferase. A special place among the enzymes involved in the neutralization of xenobiotics, inactivation of normal metabolites, drugs, is occupied by glutathione transferases (GT). 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, HTs are mainly localized in the cytosol, but there are enzyme variants in the nucleus and mitochondria.
Glutathione is a tripeptide Glu-Cis-Gly (the glutamic acid residue is attached to the cysteine by the carboxyl group of the radical). HTs have a wide specificity for substrates, the total number of which exceeds 3000. HTs bind very many hydrophobic substances and inactivate them, but only those that have a polar group undergo chemical modification with the participation of glugathione. That is, the 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 in three ways. different ways:
by conjugation of 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 detoxification system involving GT and glutathione plays a unique role in the formation of the body's resistance to various influences and is the most important defense mechanism of the cell. During the biotransformation of some xenobiotics under the action of GT, thioesters (RSG conjugates) are formed, which are then converted into mercaptans, among which toxic products have been found. But GSH conjugates with most xenobiotics are less reactive and more hydrophilic than the parent substances, and therefore less toxic and easier to remove from the body.
HTs, with their hydrophobic centers, can non-covalently bind a huge amount of lipophilic compounds (physical neutralization), preventing their penetration into the lipid layer of membranes and disruption of cell functions. Therefore, HT is sometimes referred to as intracellular albumin.
GT can covalently bind xenobiotics, which are strong electrolytes. Attachment of such substances is "suicide" for GT, but an additional protective mechanism for the cell.
Acetyltransferases, methyltransferases
Acetyltransferases catalyze conjugation reactions - the transfer of an acetyl residue from acetyl-CoA to the nitrogen of the -SO2NH2 group, for example, in the composition of sulfonamides. Membrane and cytoplasmic methyltransferases involving 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 reactions). Epoxide hydrolase (epoxide hydratase) adds water to the epoxides of benzene, benzpyrene 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 the reactions of non-enzymatic alkylation of DNA, RNA, proteins. Chemical modifications of these molecules can lead to the transformation of a normal cell into a tumor cell.
ROLE OF PROTEINS IN NUTRITION, NORMS, NITROGEN BALANCE, WEAR COEFFICIENT, PHYSIOLOGICAL PROTEIN MINIMUM. PROTEIN INSUFFICIENCY.
AK contain almost 95% of all nitrogen, so they maintain the nitrogen balance of the body. nitrogen balance- the difference between the amount of nitrogen supplied with food and the amount of nitrogen excreted. If the amount of incoming nitrogen is equal to the amount of nitrogen released, then nitrogen balance. This condition occurs in a healthy person with a normal diet. The nitrogen balance can be positive (more nitrogen enters than is excreted) in children, in patients. A negative nitrogen balance (nitrogen excretion prevails over its intake) is observed during aging, starvation, 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 corresponds to 30–50 g/cyt, while the optimal amount for moderate exercise is ∼100–120 g/day.
amino acids, the synthesis of which is complex and uneconomical for the body, is obviously more profitable to get 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 essential amino acids are necessary for their synthesis. Tyrosine is synthesized from phenylalanine, and the sulfur atom of methionine is required for the formation of cysteine.
The remaining amino acids are easily synthesized in cells and are called nonessential. These include glycine, aspartic acid, asparagine, glutamic acid, glutamine, series, pro
