CARBOXYPEPTIDASES (peptidil-amino-acid hydrolases; KF 3.4) — group of the proteolytic enzymes which are chipping off the amino-acid remains from proteins and C-trailer peptides; take part in intracellular disintegration of proteins and perform regulatory function, participating in education and an inactivation of biologically active peptides, and also in a proteopepsis. In addition to a peptide bond, To. hydrolyze also ester group in synthetic substrates of a certain structure, i.e. have esterazny activity. A necessary condition for action To. presence at substrate of free alpha COOH - group is. To. differ on the specificity on the basis of what they are subdivided into carboxypeptidases A, B, C etc.
To. are eurysynusic in various animal fabrics and are found in plants and microorganisms. Carboxypeptidases A (KF 126.96.36.199) and V (KF 188.8.131.52) from a pancreas of the highest animals and the person are the most well studied. Carboxypeptidases A and B are synthesized in a pancreas in the form of inactive predecessors — pro-carboxypeptidases A and B which, getting into a duodenum, are activated under the influence of trypsin. In the course of activation there is a hydrolysis of several peptide bonds in molecules of pro-carboxypeptidases A and B and dissociation of these proferments on subunits, one of which turns in corresponding To. At the same time as a result of hydrolytic decomposition of two-three peptide bonds in N-trailer area of this subunit several forms K can be formed. (Aα, Aβ, Aγ). Pancreatic To. the person and animals take part in digestion, splitting products of primary proteopepsis to amino acids.
The enzymes relating to group K., are metalloproteins (see), though some fabric To., unlike pancreatic carboxypeptidases A and B, are not metalenzymes, and belong to group serinovy, or SH dependent, proteinases (see. Peptide-hydrolase ). In structure of a molecule K. one Zn atom enters 2+ . It can be replaced with Mn 2+ , Co 2+ , Ni 2+ without essential to treason niya of activity of enzyme; To. during the replacement of Zn 2+ on Cd 2+ and Hg 2+ lose peptidazny and keep esterazny activity. Primary and spatial structure of carboxypeptidase A is completely deciphered. In formation of its active center, except Zn atom 2+ , the remains glutaminic to - you, tyrosine and arginine take part. The optimum of effect of this enzyme is at pH 7,5; at pH lower than 6,0 enzyme are inactivated. Carboxypeptidase A chips off from proteins and peptides all C-trailer amino acids, except arginine, a lysine, proline and oxyproline. Inhibitors of carboxypeptidase A are the substances forming inner-complex (chelate) compounds with metals (8 oxyquinoline, 1,10 phenanthroline, α,α '-dipiridil, etc.); its competitive inhibitors are β-fenilpropionovy and alpha-toluic to - you and some of their analogs. Pancreatic carboxypeptidase B is close on properties to carboxypeptidase A, but it catalyzes eliminating from peptide chains only of C-trailer main amino acids — arginine, a lysine and ornithine. Carboxypeptidases A and B are the related proteins having a homologous structure and the same three-dimensional structure. Inhibitors of carboxypeptidase B are the connections forming chelate complexes with metals; competitive inhibitors — ε-aminocaproic to - that to - that to - that, piperidic to - that and other similar connections.
In animal fabrics are found kateptichesky To., on substrate specificity the similar to carboxypeptidase A, but differing from it in an optimum activities which is at acid pH values. Along with them the specific prolylcarboxypeptidases which are selectively chipping off the S-trailer amino acids standing near the rest of proline meet.
Is present at a blood plasma of the person and animals To. (carboxypeptidase N, a kininaza of I), on the substrate specificity similar to carboxypeptidase B. This To. is also metalenzyme, active at neutral pH values. It causes an inactivation of biologically active peptides (bradikinin and its analogs) possessing hypotensive action, catalyzing eliminating from their molecules of S-trailer arginine; thereby this To. participates in regulation of blood pressure. Carboxypeptidase N of plasma of the person causes also an inactivation of the anaphylatoxins which are formed at activation of system of a complement.
See also Enzymes .
Bibliography Dickson M. and Webb E. K. Enzymes, the lane with English, page 400, etc., M., 1966, bibliogr.; Mosolov V. V. Proteolytic enzymes, M., 1971, bibliogr.
L. A. Lokshina.