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MALATE DEHYDROGENASE [L malate: OVER + (NADF +) oxidoreductase] — the enzyme catalyzing oxidation-reduction transformation of malate and oxaloacetate, and also oxidizing decarboxylation of malate to pyruvate; treats the oxidoreductases operating on CH — OH group of hydrogen donator, an acceptor to-rogo are NAD+ or NADF + (KF 1.1.1); activity of enzyme in blood serum is used in greed of auxiliary diagnostic test at a number of diseases, hl. obr. diseases of cardiovascular system and liver.

The m is one of key enzymes of a cycle Tricarboxylic to - t (see. Tricarboxylic acids cycle ); its participation in exchange dicarbonic to - t (except malate and oxaloacetate, M. oxidizes also some other 2-hydroxydicarbonic to - you, napr, shchavelevoglikolevy and alpha and hydroxyglutaric) explains that important role, to-ruyu M. plays in exchange of fats, carbohydrates and proteins.

M it is active only concerning L-isomers. This enzyme is spread in the nature very widely. In a human body and animals M.'s activity is highest in a liver, kidneys, a cardiac muscle, skeletal muscles and a brain (in decreasing order of activity).

Pier. M.'s weight, according to Dickson (M. of Dixon) and Webb (E. S. of Webb), is equal to 52000 — 62000. Optimum size pH 6,9; The Isoelectric point also is at pH 6,9. Ions of heavy metals it is irreversible inhibit enzyme.

There are two isoenzyme (see) M., one of which is localized only in mitochondrions, and another — in cytoashes (cytoplasm). M.'s isoenzymes represent genetically independent proteins. Parallel formation of enzyme in and out of mitochondrions is connected, apparently, with a problem of availability of substrate to key enzymes.

One of the main distinctions between two isoenzymes of M. consists in types of their inhibition excess of substrate. Mitochondrial M. is inhibited by excess of oxaloacetate, and the cytoplasmatic isoenzyme of M. pe is inhibited whereas excess of malate much more oppresses cytoplasmatic M., than mitochondrial. Though the reactions catalyzed by M. are reversible, these data give the chance to assume that in mitochondrions oxidation of malate is more favorable, and out of mitochondrions recovery of oxaloacetate is more preferable. Assume also that existence of two isoenzymes of M. is important for transfer of recovery equivalents from cytoplasm in a mitochondrion. M. working in opposite directions, can combine oxidation of NAD-N in cytoplasm with recovery of NAD+ in mitochondrions provided that malate and oxaloacetate freely pass a mitochondrial membrane, however it is a little probable and, obviously, in this process is accompanied by M. corresponding work aminotransferases (see) which, M. is similar, have cytoplasmatic and mitochondrial isoenzymes.

M.'s emergence in blood serum is extremely sensitive test testimonial of destruction of cells, penetration of this enzyme at first in intracellular liquid, and then in blood. Definition of the nature of an isoenzyme of M. which appeared in blood in abnormally large numbers helps to understand character patol, process at the cellular level. Normal M.'s activity in blood serum is low: 50 — 104 pieces/ml (take its such quantity for an activity unit of enzyme, a cut catalyzes transformation 1 mkmolya substrate in 1 min. at 37 °). Increase in activity of M. in blood serum is noted at a myocardial infarction, an intravascular hemolysis, hepatitises, cirrhoses, diseases of biliary tract, megaloblastichesky anemia.

It should be noted, however, that definition of activity of M. in the diagnostic purposes is applied less than definition of activity lactate dehydrogenases (see) and its isofermental range.

Methods of definition of activity of M. in biol, liquids, in cuts of fabrics and bodies — see. Dehydrogenases .

See also Oxidoreductases .

Bibliography: Biochemical methods of a research in clinic, under the editorship of A. A. Pokrovsky, page 109, 588, M., 1969; L and shouting and And. Regulation of exchange processes, the lane with English, page 362, M., 1970; Mossd.V., and Battervortp. J. Enzymologies and medicine, the lane with English, page 174, M., 19 78; The Nomenclature of enzymes, under the editorship of A. E. Braunstein, page 41, M., 19 79.

N. G. Budkovskaya.