AMINOTRANSFERASES

From Big Medical Encyclopedia

AMINOTRANSFERASES (synonym transaminases; outdated name transaminases) — the enzymes from a class of transferases catalyzing reaction of transamination, i.e. transfer of an amino group (— NH 2 ) and hydrogen atom from one molecule of substrate to another; play an important role in a nitrogen metabolism. General scheme of reaction:

Reaction proceeds without transient formation of ammonia. Enzymatic transamination was opened in 1937 by A. E. Braunstein and M. G. Kritsman which showed that drugs from a pectoral muscle of a pigeon catalyze a reversible test of education glutamic acid (see) and α-ketonic acids ((((((((((see. Ketonic acids ) from α-ketoglutarate and various amino acids.

And. are found in all studied fabrics of plants and animals and in cells of microorganisms. It is known apprx. 50 A., which affect selectively natural α-amino acids and many β-, γ-and δ-amino acids.......... The most active and the most widespread And. use glutaminic and α-keto-glutaric acids as one of donor-acceptor couples; other amino acids transaminirutsya by less active And., usually showing group specificity (see. Enzymes ) to several substrates of a similar structure, e.g. to amino acids with a branched chain or to aromatic amino acids. In bodies of the highest animals (muscles, heart, a liver) aspartate-ketoglutarate-aminotrapsferazy and alanines-ketoglutaratamino-transferases are most active.

All cleared And., allocated from fabrics of animal, higher plants and many microorganisms, stereo-are specific. They catalyze, as a rule, transamination amino acids (see) only a L-row. However are known And. some bacteria which affect only D-amino acids and do not affect their L-isomers.

As donors of amino groups serve not only α-amino acids.......... So, in tissues of animals and are found in microorganisms And., carrying out transamination of β-alanine, γ-aminobutyric and some other amino acids with α-keto-glutaric ((((((((((is more rare from pyroracemic) to - that. One of the main ways of metabolism γ-aminobutyric to - you to - you to - you in a brain are its transamination with α-ketoglutarate, therefore the glutamate and half aldehyde of succinic acid is formed (similar reaction takes place at bacteria). the δ-amino group of ornithine and aminolevulinic to - you can be also transferred And. on ketonic acids. The glutamine and asparagine react (with participation And.) with various ketonic acids with formation of the corresponding amino acids and amides (see) keto-glutaric and oxalacetic acids.

Behind the few exceptions of A. Imeyut a wide rn-optimum with a maximum in the area 8 — 9. Coenzymes And. derivatives of rat anti-acrodynia factor — pyridoxal phosphate and piridoksaminfosfat are. According to A. E. Braunstein and M. M. Shemyakin's theory, amino acid react with the pyridoxal phosphate (connected to a proteinaceous part of a molecule A.) with formation of intermediate aldimin of pyridoxal phosphate (Schiff bases) and tautomeric to them ketpmpn of a piridoksaminfosfat:

The ketimine formed thus then is hydrolyzed with release of ketonic acid. to the corresponding initial amino acid, and piridoksaminfosfata:

Further piridoksaminfosfat interacts with other ketonic acid, and all stages of reaction repeat, proceeding in the opposite direction. The initial form of a proteid of pyridoxal phosphate and new amino acid is as a result formed. Summing up, we receive: enzyme-pyridoxal phosphate + aminokislota1fermentpiridoksaminfosfat + ketokislota1 enzyme-piridoksaminfosfat + ketokislota2 enzyme-pyridoxal phosphate + aminokislota2.

Spectral researches A. showed that the pyridoxal phosphate connected with protein exists not in the form of free aldehyde, and in the form of Schiff base (see. Schiff basis ).

Formation of Schiff base between pyridoxal phosphate and an apoenzyme explains the fact that pyridoxal phosphate dissociates more difficultly from And., than piridoksaminfosfat.

And. participate in the following transformations: formation of amino acids from ketonic acids and reverse transformation (an oxidative breakdown of amino acids); biosynthesis γ-aminobutyric to - you to - you to - you, urea, the purine and pirimidinovy bases, porphyrines, flavins, pteridines, cobalamine.

Reversible formation of alanine, aspartate and glutamate from the corresponding ketonic acids is the important link which is directly connecting exchange of carbohydrates with exchange of amino acids.

And. play the main role in nitrogen metabolism (see). Oxidizing deamination of amino acids (except for a glutamate) in an animal organism is carried out through reactions of transamination taking into account wasps - keto-glutaric to - you as a carrier of amino groups. At first amino acids transaminirutsya with keto-glutaric to - that. Formed at the same time glutaminic to - that is deaminized under the influence of a glutamatdegidrogenaza with formation of free ammonia and release keto-glutaric to - you. Reversibility of the described reactions provides a possibility of synthesis of amino acids from ammonia and ketonic acids by indirect amination of the last. After transition of nitrogen glutaminic to - you in asparaginic to - that under action And. nitrogen of aspartate is used in various processes of biosynthesis, dissimilirutsya in other enzymatic transformations to end nitrogenous products (ammonia, urea, uric to - that). Definition of activity And. in blood and other biological liquids has a certain diagnostic value. So, contents And. sharply increases in a blood plasma of patients at some morbid conditions which in particular are followed by destructive processes in parenchymatous bodies. So, e.g., contents And. (and first of all asparat-ketoglutarates-aminotransferases) in a blood plasma of the patient increases repeatedly at a myocardial infarction, reaching a maximum on the second and third day. It allows to carry out the differential diagnosis (in particular, from an attack of stenocardia, at Krom activity And. in plasma does not raise). Similarly at a viral hepatitis from the struck cells of a liver a large number comes to a blood plasma And., in particular alanines-ketoglutarates-aminotransferases that is not observed at other forms of jaundice (e.g., obstructive). At a viral hepatitis and other defeats of a parenchyma of a liver definition And. in a blood plasma has not only diagnostic, but also predictive value.

See also Transferases .



Bibliography: Molecular bases of action and braking of enzymes, Works of the 5th International biochemical congress, Symposium 4, M., 1962; Guirard B. M. and. Snell E. E. Vitamin B6 function in trans-amination and decarboxylation reactions, Cpmprehens. Biochem., v. 15, p. 138, 1964, bibliogr.


G. A. Kochetov.

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