PHOSPHORIC EXCHANGE

From Big Medical Encyclopedia

PHOSPHORIC EXCHANGE — set of reactions of transformation of mineral phosphorus and the organic phosphorus compounds occurring in an organism. At animals, plants and microorganisms F. the lake is important for ensuring all processes of life activity. Biol. role F. by the lake it is connected with involvement of the inorganic phosphorus (see) which is a part of foodstuff, a metabolism and energy (see) in a cell. Turning into ethers of organic compounds, inorganic phosphorus (Fn) participates in synthesis of various functionally important components of a cell, including the high-energy phosphoric connections (see. Vysoko-ergichesky connections) which are continuously used during the performance of various work: mechanical — reduction of muscles (see. Muscular contraction), electric — pe

a redacha of nervous impulse (see. A nervous cell), transport — functioning of glands, intestines, kidneys, etc., chemical — the processes of synthesis demanding energy consumption. Activity of a number of enzymes F. the lake in blood, urine, etc. is a valuable .diagnostichesky sign, and genetically caused insufficiency of the nek-ry enzymes catalyzing reactions F. the lake, is the reason of serious hereditary diseases (see).

Pathways of phosphorus compounds. Fn and phosphorus substances of foodstuff are exposed to turning into a digestive tract. Organic phosphorus compounds are split under the influence of esterases (see) and phosphatases (see) digestive juices, and 70 — 90% of the phosphate which got to an organism with food are soaked up in a small bowel. Assimilation of Fn depends on contents in food of proteins (see), fats (see) and calcium (see). Fn of milk, a ratio between the maintenance of Fn and calcium in Krom about 1:1V3 is best of all acquired. Phosphate salts of Sa3(r04) calcium 2, Sanr04, Sa (H2P04)2 participate in a mineralization of bones. The main part of phosphate salts (apprx. 85%) is laid in bones in a type of Sa3(r04)) 2 and the Ca10(PO4) fi (ON) hydroxylapatite 2 which is formed in the course of a mineralization of bones. Between Fn of bones and blood there is a constant exchange: per day exchanges apprx. 10 — 20% of phosphate of a bone tissue (see. Mineral metabolism).

Come to blood generally or-to-and a pyrophosphate (see. Phosphoric acids) and a nek-swarm the amount of organic phosphate, the most part to-rogo contains in erythrocytes. In a blood plasma concentration of Fn is maintained on a fixed level and makes

2,5 — 6 mg at adults! 100 ml, at newborn 4,2 — 8 mg! 100 ml, children have 1 month — 2 years —

4 — 7 mg! 100 ml, 2 — 14 years —

2 — 5 mg! 100 ml. Anions phosphoric to - you are HPOjj and H2P04, the ratio to-rykh is equal in a blood plasma about 4:1, are an essential part of buffer system of blood and others biol. liquids of an organism. From extracellular liquid in a cell of Fn passes through a cellular membrane against a gradient of concentration (see Transport of ions), however the mechanism of active transport of Fn is unknown. Fn through kidneys and intestines is removed. Excretion of phosphate kidneys plays an important role in maintenance of acid-base equilibrium (see). The mechanism of maintenance of concentration of hydrogen ions in an organism is connected with process of formation of urine (see) and consists in change of a ratio between one - and disubstituted phosphate Na2HP04 and NaH2P04 sodium salts; H2P04 anions make the main part titrated in urine to - you.

Participation of Fn in power and plastic exchanges in a cell is carried out in various ways. One of the major metabolic ways such is carbohydrate and phosphorus exchange, intermediate products to-rogo join in exchange of fats (see the Lipometabolism), proteins (see. Nitrogen metabolism), nucleic acids (see) and other substances. Carbohydrate and phosphorus exchange can be divided into synthesis and disintegration of a glycogen (see), anaerobic and aerobic transformation of glucose (see Glycolysis) and a gluconeogenesis.

The most intensive synthesis of a glycogen, the catalyzed glycogen synthase (KF 2.4.1.11), proceeds in a liver, and also in the muscles which are in rest. In disintegration of a glycogen the major role is played by a phosphorolysis (see). Under the influence of enzymes of phosphorylases (see) glyukozo-1-phosphate is formed, to-ry then turns into gluco-zo-6-phosphate. In a liver the last is split by glyukozo-6-phosphatase (KF 3.1.3.9), and free glucose (see) comes to a blood channel and then to fabrics. One of the most important products of glycolysis is ATP. Transformation of one molecule of glucose in the course of F. the lake, including a cycle tricarboxylic to - t (see Trikarboio-vy acids a cycle) and oxidizing phosphorus silt an irovaniye in a respiratory chain (see biological oxidation), leads to synthesis of 38 molecules ATP.

The gluconeogenesis — synthesis of glucose — proceeds in is woven a liver and kidneys. Generally it occurs due to reversibility of reactions of glycolysis. The irreversible reactions of glycolysis catalyzed by a hexokinase, fosfo-fruktokinazy and a pyruvatekinase (see Kinases), are replaced with other reactions which are completely providing process of a gluconeogenesis. In a liver there are systems of phosphorylation (see) not only glucose, but also fructose (see) and galactoses (see).

The carbohydrate metabolism (see) on a pento-zofosfatny way proceeding in a liver, kidneys, embryonal fabrics, the mammary gland which is drawing up l, is important for plastic metabolism of substances. Products of a pentozofosfatny metabolic way — pentozofosfata and the recovered NADF (NADF-N2) are used for biosynthesis of various components of a cell: fatty acids (see), cholesterol (see), nucleotide coenzymes (see), nucleic acids (see), etc. The anaerobic stage of a pentozofosfatny way is closely connected with glycolysis. Depending on requirement of a cell process proceeds or in the direction of accumulation of phosphopentoses, or accumulation of products of glycolysis — fruktozo-6-phosphate and a glyukozo-6-fos-veil.

A lipometabolism, in particular synthesis of triglycerides (see) and phospholipids (see Phosphatides), it is closely connected with carbohydrate and phosphorus exchange. Glitserol-3-phosphate participates in synthesis of the triglycerides which are the main substrate of oxidizing exchange in an organism. Formed then fosfatidny to - that turns into triglycerides or into phospholipids — the main components of cellular membranes. Synthesis of sterols, including cholesterol, is followed by formation of fosforilirovanny intermediate products — 5-phospho-i 5-pirofosfomevalonovy to - you.

Uridinetriphosphate (UTF) and ribozo-5-phosphate participate in the synthetic reactions connected with neutralization of toxic products of exchange of proteins in a liver (cresol, phenol, an indole); at neutralization of ammonia intermediate products of synthesis of a glutamine (see) and urea (see) is glutamil-phosphate and karbamoilfosfat.

Special value F. the lake has for synthesis and disintegration of DNA (see. Deoxyribonucleic acid) and RNA (see RNA). Key synthetic reaction of purine bases (see) both pirimidinovy the bases (see) and the corresponding nucleotides, base units nucleinic to - the t is reaction of education 5-phosphoribosyl-1 - a pyrophosphate from ribozo-5-phosphate and ATP. Phosphorylation nukleozid-mono-and nukleoziddifosfat is catalyzed by specific kinases. Takes part in exchange of DNA and RNA a polinukleotidfosfori-manhole (KF 2.7.7.8) — the enzyme catalyzing transfer of the nucleotide rest to Fn. Reversibility of this reaction was used for studying of the mechanism of synthesis nucleinic to - t and interpretations of a genetic code (see) protein synthesis. At last, in the most important process — synthesis of protein by means of ATP there is an activation of amino acids; guani-dintrifosfat (GTF) participates in processes of phosphorylation at a stage of elongation (building of a poly-peptide chain) happening in a ribosome (see). Essential value for synthesis of protein has also phosphorylation of nucleoproteids (see Phosphoproteins).

Regulation of phosphoric exchange. Exchange of Fn in an organism is regulated by vitamin D (see Calciferols), hormones of epithelial bodies (see) and a thyroid gland (see). Parathormone (see) regulates the content of phosphate and calcium in blood. Strengthening of phosphate in blood serum is a consequence of influence of hormone on solubility of phosphorus-calcium salts in a bone tissue and on a reabsorption of phosphate in kidneys. The regulating effect of parathormone on a bone tissue and kidneys is connected with adenilattsiklazny system. Hormone of a thyroid gland kaljtsito-nin (see) renders on a bone tissue and on the content of phosphate in blood opposite effect: it interferes with dissolution of salts of a bone tissue and causes a hypophosphatemia (see Fosfatemiya).

Regulation F. the lake is carried out by c. N of page and corresponding hormones. Activation of carbohydrate and phosphorus exchange is connected with effect of adrenaline (see) and a glucagon (see). The hormone-receptor complex which is formed on a cellular membrane activates the adenylatecyclase (KF 4.6.1.1) catalyzing formation of cyclic nucleotides 3\5' - AMF or 3', the 5th '-guanozinmono-phosphate (according to tsAMF, tsGMF). Protein kinase (KF 2.7.1.37), dependent on tsAMF, interacting with tsAMF, it is activated and provides phosphorylation of a kinase of phosphorylase (KF 2.7.1.38) and a glycogen synthase (KF 2.4.1.11),

century the result to-rogo activity of the first enzyme increases, and the second — is oppressed. The kinase of phosphorylase in turn phosphorylates and activates a glycogen phosphorylase (KF 2.4.1.1), catalyzing splitting of a glycogen. This way of regulation of activity of enzymes F. the island leading to the whole cascade of reactions, quickly and effectively increasing the rate of decay of a glycogen (see Phosphorylases), is important especially for provision of energy the working muscles (see). More than 25 enzymes are known, activity to-rykh is regulated in the same way. Among them there is a number of enzymes F. lake of a liver (piruvatki-naz, fosfofruktokinaza and fruktozo-1,6-diphosphatase).

Many reactions F. lakes are catalyzed by allosteric enzymes. Activity of allosteric enzymes is regulated by their interaction with molecules of the substances effectors contacting a molecule of fermental protein in the sites remote from active centers. Intermediate products of exchange — metabolites, substrates, adenylic nucleotides, etc. Products F usually act as effectors. lakes can regulate biol. activity of various proteins. E.g., 2,3 diphosphoglycerate in erythrocytes are allosteric effect of hemoglobin (see). Contacting hemoglobin, it promotes return of oxygen by it to fabrics.

Disturbances of phosphoric exchange. At a lack of vitamin D the phosphorus-calcium exchange connected with process of an osteogenesis is broken and rickets develops (see). Rickets is followed by increase in concentration of phosphate in urine (see Fosfatu-riya) and reduction — in blood. Ratio distortion between phosphate and calcium leads to demineralization of bones. Bone diseases are characterized by reduction of activity of an alkaline phosphatase (KF 3.1.3.1.) in bone cells — osteoblasts and increase in its activity in blood serum; extent of increase in activity of this enzyme correlates with extent of bone defeat. At the disease of gepa-tobilparny system, malignant tumors affecting bones, activity of this enzyme also increases in blood serum. Fos-forno-kaltsiyevy exchange is broken at a hyperparathyreosis (see), a gastroenteritis (see) and diabetes (see a diabetes mellitus), causing the acidosis promoting dissolution of bones and formation of urinary stones (see).

A number of the hereditary diseases connected with genetically caused defect of enzymes F is known. lake. At glycogenoses (see) activity glyukozo-6-fos-fatazy or phosphorylases is blocked. Inborn lack of the enzyme phosphorylating fructose causes a frukto-zemiya (see), and also increase in removal with urine nemetabolizirovan-ache fructose. Lack of activity of galaktozo-1-fosfaturidilil-transferase (KF 2.7.7.10) at a galactosemia (see) is followed by strengthening of sugar in blood at the expense of a galactose and accumulation in a liver of the galaktozo-1-phosphate possessing toxic action on an organism. Hereditary dystrophy of muscular tissue is caused by disturbance of processes of phosphorylation in muscles and increase in activity of a creatine kinase and zymohexase (KF 4.1.2.13) in blood. Disturbance of synthesis of key enzymes of glycolysis — fruktokinaza, a hexokinase and a pyruvatekinase, and also oppression of activity observe a glycogen synthase at the diabetes mellitus (see a diabetes mellitus) connected with a lack of insulin.

Bi-gppovptamiioz (see Thiamin) causes oppression of activity a trance-keto manholes (KF 2.2.1.1) — enzyme of a pentozofosfatny way of carbohydrate metabolism — and is followed by disturbance of exchange of amino acids, biosynthesis of fats, cholesterol, nucleinic to - t, etc.

Damage of fabric as a result of an anoxia, ischemia, a heart attack, thromboses, etc. leads to increase in activity of a number of enzymes F. the lake in blood serum. Disturbance of reactions of power and plastic exchanges of phosphorus compounds in a myocardium is revealed at various heart diseases.

Methods of studying of phosphoric exchange. Research F. the lake in clinic is carried out by means of a blood analysis, urine and others biol. liquids. At diagnosis of many diseases define the maintenance of Fn, phosphoric connections, activity of a number of enzymes F in blood. lake. Broad application was found by tracer techniques. Administration of radioactive phosphorus (see) gives the chance to study speed F. the lake in a complete organism. Inclusion of radioactive phosphorus in various phosphorus compounds allows to investigate mechanisms and ways of their transformations, permeability biol. membranes, etc. Data on features F. the lake can be received, using biopsy material, in Krom define activity of enzymes and their isofermental structure. Maintenance of intermediate products of F.o. in blood, urine, a bone tissue, defined with the help ul-

tratsentr of a fugirovaniye (see), an electrophoresis (see), a chromatography (see), the immunochemical analysis, etc., gives full information on a state F. the lake in an organism. Research F. lakes in an experiment carry out by perfusion of bodies, receiving fabric cuts and homogenates, allocation of various cellular and subcellular structures (mitochondrions, kernels, microsomes, etc.), and also their fragments. The large number of researches is conducted on individual enzymes F. lake.

Bibliography: Berezov T. T. and To

ro in to and B. F N. Biological chemistry, M., 1982; The Clinical enzymology,

under the editorship of E. Shcheklik, the lane with polsk., Warsaw, 1966; Moss D. U. and B and t of t e r-in about r P.DZh. Enznmologiya's t and medicine, the lane with English, M., 1978; The Guide to clinical laboratory diagnosis, under the editorship of V. V. Menshikov, page 229, 560, M., 1982: Whyte A. and d river. Fundamentals of biochemistry, the lane with English, M., 1981;

Krebs E. G. and. In e a v about J. A. Phosphorylation-dephosphorylation of enzymes, Ann. Rev. Biochem., v. 48, p. 923, 1979; R a p oport S. M. Medizinische Biochemie, B., 1977. P.JT. Vulfson.

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