From Big Medical Encyclopedia

OXIDOREDUCTASES (KF 1.) - a class of the enzymes catalyzing redoxreactions; are localized in various structures of a cell, generally in mitochondrions, peroxisomas, and also in cytosol, i.e. are desmoenzymes. Change of activity and isofermental range of nek-ry O., especially dehydrogenases (see), serves as auxiliary diagnostic test at a number of diseases.

Substrates, to-rye are oxidized with the assistance of O., are considered as electron donors or hydrogen atoms. The systematic name O. according to the classification offered by the International biochemical union and the International commission on enzymes is formed according to the scheme "hydrogen donator: electron sink oxidoreductase".

The class O. includes 21 subclasses so far. Carry the enzymes operating on the SN — IT group of the donor to a subclass of 1 class of oxidoreductases (KF 1.1); to a subclass 2 (KF 1. 2) carry the enzymes operating on aldehydic or keto-groups of the donor; to a subclass 3 (KF 1. 3) carry the enzymes operating on group — CH — CH of the donor; to a subclass of 4 (KF 1.4) — the enzymes operating on CH — NH 2 group of the donor; to a subclass 5 (KF 1. 5) — the enzymes operating on C — NH group of the donor, etc.

The third figure of the classification code of enzyme of a class O. indicates (subsubclass) type of electron sink: 1 — OVER or NADF, 2 — cytochrome, 3 — molecular oxygen, 4 — a disulfide, 5 — quinone etc. The fourth figure of the classification code designates sequence number of specific enzyme in a subsubclass.

In addition to the systematic name O. have generic names. The term «dehydrogenases» is used when an acceptor of hydrogen atoms from the donor are any molecules, except oxygen.

The term «oxidases» is applied when electron sink is the molecule of oxygen (see. Oxidases ).

Systematic and generic names nek-ry NAD (NADF) - dependent dehydrogenases are given as examples in the table, activity and an isofermental range to-rykh are used in a wedge, practice as additional diagnostic test.

Depending on the nature of a cofactor of O. it is possible to divide into three groups: 1) OVER - or NADF-zavi-simye dehydrogenases; 2) flavin - dependent dehydrogenases and oxidases, in a molecule to-rykh a role of prosthetic group play FAD or fla-vinmononukleotid (FMN); 3) Tsitokhroma, containing zhelezoporfiri-new ring system as prosthetic group.

Various NAD(NADF) - dependent dehydrogenases usually easily dissociate on protein and prosthetic group (coenzyme) and are in a dynamic equilibrium with the dissolved part of NAD or NADF. It provides the interfaced action of various dehydrogenases. So, prosthetic group of one dehydrogenase, being recovered in a complex with a molecule of enzyme, can pass into solution and, being associated with other dehydrogenases, can in a complex with them recover (to hydrogenate) molecules of various acceptors (see. biological oxidation ).

Many NAD(NADF) - dependent dehydrogenases (glitseraldegid-3-fosfatdegidrogenaza, alcohol dehydrogenase, a lactate - malate - glutamatdegidrogenaza, etc.) are received in high cleaning and a crista a llichesky look. It is established that the large number of NAD(NADF) - dependent dehydrogenases has as a part of the molecule ions of bivalent metals (Mg 2+ , Mn 2+ , Zn 2+ etc.).

Measurement of speed of the enzymatic reaction catalyzed by NAD(F) - dependent dehydrogenases, is based on measurement of absorption intensity at 340 nanometers, edges increases in the course of recovery of NAD or NADF, or on measurement of the size pH, change a cut is connected with the release of a proton accompanying recovery of NAD+ or NADF +, or on measurement of fluorescence as the oxidized forms of NAD and NADF unlike them got into condition are characterized by strong fluorescence in the field of 440 nanometers. Got into condition by NAD(F) - dependent dehydrogenases are not oxidized molecular oxygen. Transfer of hydrogen by them on the corresponding acceptors happens in anaerobic conditions. As a rule, the initial stage of anaerobic oxidation of substrate is followed by reaction of aerobic oxidation of the recovered NAD (NADF) with participation of system of flavin enzymes and tsitokhrom (see. Respiratory enzymes ).

The most important role from flavin - dependent dehydrogenases is played NAD(F) • By the N-dehydrogenase, a succinatedehydrogenase and a digidrolipoil-dehydrogenase which is a part piruvatdegidrogenazny and alpha ketoglutaratdegidrogenaznogo complexes. Nek-ry flavin O. contain also, in addition to FAD and FMN, cations of metals. E.g., succinate dehydrogenase, in addition to FAD, contains in a complex connected iron. Wide ranges of absorption at 370 and 450 nanometers are characteristic of flavinzavisimy dehydrogenases. At enzymatic or chemical recovery at most of absorption in the field of 450 nanometers disappears. The oxidation-reduction process catalyzed by flavinzavisimy dehydrogenases is followed by also characteristic changes in a range of fluorescence, to-rye use during the definition of activity flavin - dependent dehydrogenases.

The Tsitokhromny system is presented various tsitokhromam (see), the absorption spectrums differing among themselves the recovered and oxidized forms and the size of redox potential. At mammals in mitochondrions b, c, c1, a3 and are found in microsomes — b5 cytochrome of Tsitokhroma. The last cytochrome of a respiratory chain, cytochrome a3, reacting with oxygen, is called cytochrome oxydase.

At a row patol, states observe change of activity and an izofer-mentny range nek-ry NAD(F) - dependent dehydrogenases. So, at nek-ry diseases of a liver (e.g., at an acute inf. hepatitis) in blood serum in the heat of a disease sharply hyperactivity lactate dehydrogenases (see) and alcohol dehydrogenase (see), and in later terms — activity of a glutamatdegidrogenaza. At acute infectious hepatitis, and also at malignant new growths observe change of an isofermental range of nek-ry dehydrogenases, including emergence of abnormal molecular forms of enzyme. Definition of activity and isofermental structure of a lactate dehydrogenase in blood serum is the important test at differential diagnosis of a myocardial infarction and overseeing by its current (see. Myocardial infarction ). Genetically caused hemolitic anemia (see) it is characterized by decrease of the activity in erythrocytes of one of oxidoreductases — NADF-zavisimoy glyukozo-6-fosfatdegidrogenazy (KF 1. 1. 1. 49), what causes reduction of formation of ATP in erythrocytes, a delay of ions of Na + and related water, swelling and hemolysis of erythrocytes. At total absence of activity of this enzyme hemolitic anemia is shown spontaneously already at children's age. Also inborn insufficiency or total absence of activity of one more O. — a glutationreduktaza can be the cause of hemolitic anemia (KF 1. 6. 4. 2), the concentration of glutathione causing pathological decrease in erythrocytes.

See also Enzymes .


Bibliography: Biochemical methods of a research in clinic, under the editorship of A. A. Pokrovsky, page 107, M., 1969; To r e of t about - in and the p B. of JI. Introduction to enzymologies), page 195, M., 1974; The Nomenclature of enzymes, the lane with English, under the editorship of A. E. Braunstein, M., 1979; Yurkov Yu. A. Clinical value of definition of isoenzymes of a lactate dehydrogenase and malate dehydrogenase, in book: Probl, medical chemical, under the editorship of V. S. Shapot and E. G. Larsky, page 37, M., 1973; Witteveen S. And. and. lake of Quantitation of infarct size in man by means of plasma enzymes levels, Brit. Heart J., v. 37, p. 795, 1975.

I. S. Severin.