From Big Medical Encyclopedia

CATALASE (H 2 O 2  : H 2 O 2 - oxidoreductase, KF — the enzyme catalyzing decomposition reaction of hydrogen peroxide on water and molecular oxygen. Biol, a role consists in destruction of the hydrogen peroxide which is formed in cells as a result of action of a number of flavoproteinovy oxidases (a xanthineoxidase, glucose oxydas, monoamine oxidase, etc.). Presence To. provides effective protection of cellular structures against degradation under the influence of hydrogen peroxide. Genetically caused insufficiency To. is one of the reasons of a hereditary disease at the person.

Catalytic disintegration of hydrogen peroxide in the presence of animal and vegetable fabrics or their homogenates for the first time was observed by Tenar (L. J. Thenard, 1818). Is later Shenbeyn (Ch. F. Schonbein, 1863) explained process of decomposition of hydrogen peroxide with living tissues effect of enzyme which was emitted in 1901. Left (O. Loew), called its catalase.

To. it is eurysynusic in tissues of animals and plants and in microorganisms. Contents To. in a liver and erythrocytes of mammals makes 0,1 — 0,2%, in separate strains of microorganisms — to 5% of dry weight. Enzyme completely is absent at some anaerobic microorganisms. In plants To. is present at small amounts.

Technique of allocation To. it is based on consecutive fractionation of extracts of animal and vegetable fabrics by organic solvents and ammonium sulfate. First crystal drug K. it was received by Sumner (J. Century of Sumner) in 1937.

To. is a hemoprotein, as its prosthetic group serves ferriprotoporfirin IX, the containing trivalent ion of iron. Molecule K. consists of four probably identical subunits and has respectively four prosthetic groups. Ferriprotoporfirinovy groups are strongly connected with an apoenzyme and do not separate from it at dialysis. To., allocated from a liver or erythrocytes of mammals, has coefficient of sedimentation 11,1 — 11,8S, an isoelectric point at pH 5,4 — 5,8 and a pier. the weight (weight) apprx. 240 000. Except a strip of absorption, characteristic of proteins, at 280 nanometers, in an absorption spectrum To. there is an intensive strip at 400 — 409 nanometers (a strip Soar) and strips with maxima at 622, 540, 500 nanometers caused by existence of prosthetic groups.

To. decomposes hydrogen peroxide with exclusively high speed. At pH 7,0 and t ° 20 ° one molecule K. decomposes up to 105 molecules H in a second 2 O 2 . An optimum pH value for To. lies in the range of 6,0 — 8,0. The standard mechanism of action To., the offered Chansom (V. of Chance, 1948), assumes formation of an intermediate complex of enzyme with H 2 O 2 («connection I») which interacts then with the second molecule of hydrogen peroxide. Formation of «connection I» can be registered by a spectral technique on decrease in absorption intensity in a strip Soar. «Connection I» can also interact with various hydrogen donators (ascorbic to - that, phenols, methyl and alcohol, etc.), oxidizing them for account H 2 O 2 . In this case To. shows peroksidazny activity (see. Peroxidases ). Except H 2 O 2 , To. it is capable to form primary complexes with hydroperoxides of methyl and ethyl.

Activity To. it is inhibited by cyanide, fluoride, azide, sulfide, acetate, 3-amino-1,2,3-triazole and its analogs. To. it is quickly inactivated in solution at pH more than 10,0 and less than 4,0 and in the presence of high concentration of urea or other hydrogen bindings of agents causing a gap. The inactivation of enzyme is connected with formation catalystically of inactive subunits.

Methods of definition of activity To. concentration of hydrogen peroxide are based on registration formed in the course of reaction 02 (manometrical or polyarografichesky by methods) or on measurement flowing (spektrofotometrichesky) or residual (permanganatometrichesky, yodometrichesky and other methods). As H 2 O 2 is the strong oxidizer inactivating enzyme, definition of activity To. carry out at low concentrations of substrate and t ° 0 — 10 °. For definition of activity To. in blood widely use Bach's method — Zubkova (see. Baha — Zubkova a method ).

Activity To. in erythrocytes remains not changed at a number of diseases, only at malignant anemia and other macrocytic anemias the so-called Katalazny index increases (the katalazny activity of a certain volume of blood divided into quantity of erythrocytes in this volume in one million). At malignant new growths reduction of activity is noted To. in a liver and in kidneys, and there is a dependence between the size and growth rate of a tumor and extent of reduction of activity To. in a liver. From some tumors fractions which at introduction by an experimental animal caused in them decrease of the activity To are allocated. in a liver. These fractions were called toksogormona.

At hereditary insufficiency To., inherited on recessive type, the disease carrying the name an akatalaziya and consisting in lack of activity To develops. or strongly lowered its activity in blood serum (see. Akatalaziya ). This disease is characterized by an ulceration of a mucous membrane of a nose and mouth, sometimes with the expressed gangrenous changes.

Bibliography: Kraynev S. I. About forms of a catalase in erythrocytes of the person, Biochemistry, t. 35, century 4, page 662, 1970, bibliogr.; Mikhlin D. M. Biochemistry of cellular respiration, M., 1960; O. M. half-torak and E. S. O Chukhray mechanism of action of a catalase, Vestn. Mosk. un-that, it is gray. chemical, Nt 6, page 656, 1971; Enzymes, under the editorship of A. E. Braunstein, page 215, M., 1964; Takahara S. Progressive oral gangrene probably due to lack of cata-lase in blood (acatalasaemia), Lancet, v. 2, p. 1101, 1952.

Yu. M. Azizov.