PEROXIDASES

From Big Medical Encyclopedia

PEROXIDASES — group of the oxidation-reduction enzymes (KF 1.11.1.1 — 1.11.1.10) using hydrogen peroxide as electron sink (H 2 O 2 ); catalyze reaction:

Biol, value P. is defined by their participation in oxidation of various substrates on membranes of mitochondrions and microsomes. The main biol, vegetable P.' substrates are polyphenols (see). Catalyzing oxidation of polyphenols with the participation of H 2 O 2 , P. take part in process of breath of a plant cell. At animals and the person P. also take part in a number of the oxidizing processes proceeding in fabrics. So, P. in the presence of H 2 O 2 catalyze oxidation of adrenaline, a histamine, fat to - t, nucleotides, iodide. The iodide ion which is formed as a result of peroksi-dazny oxidation iodine is used in the course of synthesis of hormone of a thyroid gland — thyroxine. The item of a thyroid gland, except oxidation of iodide, catalyzes also covalent binding of the diyodotirozinovy remains leading to formation of thyroxine. Lacto-peroxidase and P. of leukocytes catalyze peroxide oxidation of lipids in the presence of H 2 O 2 and 1 ~. Assume that such systems give antimicrobic activity to milk, saliva and polymorphonuclear leukocytes. The degree of activity of P. serves as the additional test at diagnosis of an acute miyeloblastny leukosis in leukocytes. Items of saliva play a part in a pathogeny of periodontosis. Definition of activity of P. in saliva is used as the auxiliary test at diagnosis of periodontosis and for control of efficiency of its therapy.

Contains in tissues of animals active glutathione peroxidase. In a liver destruction of H is connected with effect of this enzyme 2 O 2 , which is formed as a result of activity of various oxidases. The reaction catalyzed by glutationperoksidazy is connected with oxidation of glyukozo-6-phosphate and simultaneous recovery of the oxidized glutathione which is formed at recovery of H 2 O 2 in peroxidase reaction. Oxidation got into condition pyridinic nucleotides by system O is described 2 — Mn 2+ — Peroxidase.

Items use for kliniko-biochemical analysis as one of components of reaction mixture during the determination of content of glucose in biol, liquids by a glyuko-zooksidazny method (see. Gorodetsky methods ).

Peroxidase reaction was opened in 1855 for Shenbeynom (Ch. F. Schonbein), and the name of this group of peroxidases enzymes offered in 1898 Mr. of Linossye (M. Linossier).

Items are eurysynusic in an animal and flora. In large numbers they contain in roots of horse-radish and a turnip, in natural latex of a fig tree. At animal P. are present at milk, a liver, a mucous membrane of guts, sialadens, leukocytes, erythrocytes.

Physical. - chemical and biol, properties P. are studied on the example of peroxidase most in detail from roots of horse-radish which in 1941 was received by X. Teorell in a crystal look.

Items represent hemoproteins about a pier. it is powerful (weighing) from 40 000 to 100 000. The possibility of reversible separation of an apoenzyme from prosthetic group which is protohematin was shown. Addition of pure protohematin to P.'s apoenzyme caused almost complete recovery of activity of enzyme. It is established that in the course of peroxidase reaction the oxidized substrate joins directly atom of iron of prosthetic group of enzyme. Peroksidazny activity (though rather weak) also hemoglobin has; this its property is used for express definition of presence of blood or hemoglobin, napr, in urine, and also by identifications of traces of blood in court. - medical practice.

Pure P.'s solutions have characteristic maxima of absorption in the visible range of a range at 645, 583, 548 and 498 nanometers.

Items show high specificity to peroxide group and in many cases are a little specific in relation to hydrogen donator (except for bacterial P. and peroxidase from a peanut). For lack of hydrogen donator (the oxidized substrate) P. form complexes with H 2 O 2 , what is followed by change of an absorption spectrum of enzyme. Items form with H 2 O 2 four types of the complexes which are easily found spektrofotometrichesk (see. Spektrofotometriya ). The complex I is formed at once at addition H 2 O 2 to enzyme also represents unstable connection of green color, a cut usually quickly turns into a complex II of light-red color. At surplus of H 2 O 2 complexes III and IV — connections of dark red color are formed. These complexes are catalystically inactive, their education leads to a genaktivation of enzyme.

The item concerning a termostabilna. In low concentrations they are inhibited by so-called respiratory poisons (cyanide, azides, sulfide) connecting iron in humic groups P. and also hydroxylamine, thiourea, nitric oxide.

P.'s activity can be determined by quantity pyrogallol (see), the oxidized H 2 O 2 in the presence of enzyme. Oxidate of pyrogallol purpurogallin is extracted after sedimentation of protein from incubatory mix ether and defined photometric. About P.'s activity judge by the calculated amount of the purpurogallin (Pur-nurogallinovoye number) formed at action of 1 mg of dry fermental drug within 5 min. at 20 ° of 5 g of the pyrogallol dissolved in 2 l of the water containing 10 ml of 0,5% of solution H 2 O 2 .



Bibliography: Barabash R. D., etc. A role of peroxidase in a pathogeny of periodontosis, Vopr. medical chemical, t. 25, No. 3, page 333, 1979; Dickson M. and At e E. Enzymes, the lane with English, page 96, etc., M., 1966; The Nomenclature of enzymes, the lane with English, under the editorship of A. E. Braunstein, page 75, M., 1979.


I. V. Verevkina.

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