DECARBOXYLASES — enzymes of a class LiAZ, groups C — C-liaz (KF 4.1.1.); catalyze reactions of decarboxylation, i.e. eliminating of carbon dioxide (CO 2 ) from a carboxyl group of amino acids and ketonic acids. Some D.' insufficiency is the reason of a hereditary alpha ketoaciduria, many D. are used in kliniko-biochemical laboratories for quantitative definition of amino acids, receiving biological active amines, etc.
of D. of amino acids is the complex enzymes consisting of an apoenzyme (protein) and a coenzyme. For all amino acids studied by D. a coenzyme is phosphorylations the form of vitamin B 6 — piridoksal-5 '-phosphate. The drugs D. of amino acids inactivated by dialysis or other influences completely recover the activity in the presence of this coenzyme. Native D. of amino acids (choloenzymes) have a maximum of absorption at 415 nanometers that is characteristic for connected with protein piridoksal-5' - phosphate. In A. E. Braunstein's laboratory it was shown that D.'s activity cysteic to - you is not found in a liver of Wb-avitamonous rats, but very quickly appears in it at treatment of avitamonous animals a pyridoxine. Thus, D. of amino acids are pyridoxal phosphate - dependent enzymes. The exception is made by a histidinedecarboxylase (KF 188.8.131.52) of some bacteria and the karnitindekarboksilaza which is recently found in a cardiac muscle. According to Snell (E. E. Snell) with employees (1972), in molekulegistidindekarboksilaza a role of a coenzyme carries out the pyruvate which is structurally connected with an apoenzyme. Of amino acids strictly of a stereokhimicheska are specific and catalyze decarboxylation (see) only L - alpha amino acids.
The chemical mechanism of action of D. of amino acids is explained by the general theory of effect of the pyridoxaleft enzymes developed by A. E. Braunstein, M. M. Shemyakin and Snell.
In 1973 Mr. G. D. Pietra and employees described properties of a specific ornithinedecarboxylase (KF 184.108.40.206) allocated from a prostate of the person. The reaction catalyzed by this D. is the limiting stage of process of biosynthesis of the polyamines which are contained in high concentration in a prostate of the person. Activity of enzyme is regulated by reaction product — putrestsiny.
In a prostate of the person one more specific enzyme catalyzing decarboxylation of S-аденозил-L-methionine — the predecessor of polyamines is found: the formed reaction product is a donor propyl - the amine group used together with putrestsiny at biosynthesis of spermidine being the predecessor of spermine. This enzyme is found also in microorganisms.
E. F. Gale managed to show that some strains of bacteria E. coli, V. of cadaveris, Clostridium welchii and C1, septicum contain 5 various strictly specific D. operating on L-isomers of arginine, ornithine, a histidine, lysine and glutaminic to - you with formation of the corresponding amines. At a bacterium of Streptococcus faecalis it is found specific by L - tirozinde-karboksilaza (KF 220.127.116.11). The highly sensitive way of quantitative definition of separate amino acids developed by Gale is based on property of some bacteria to specifically decarboxylize strictly certain amino acids.
Bacterial D. of amino acids find practical application in biochemical, laboratories for quantitative definition of amino acids, for receiving the amines which are possessing biol, activity and found broad application in medical practice (a histamine, etc.), and also for receiving D-isomers of amino acids by decarboxylation of L-amino acids in their racemic substances.
Decrease of the activity of D. of amino acids with a branched chain — a leucine - and valinedecarboxylases
(KF 18.104.22.168) is one (if not main) from the reasons of an alpha ketoaciduria — the disease caused by defects of a catabolism of a leucine (see. Dekarboksilaznaya insufficiency ).
Bibliography: see bibliogr, to article Decarboxylation .
T. T. Berezov, 3. S. Kagan.