PAPAIN (synonym papainaza) — proteolytic enzyme (KF 184.108.40.206), concerns to group peptide-hydrolases, contains in natural latex of a melon tree — Carica papaya. The item splits various proteins and peptides, and also synthetic substrates — amides and esters of the N-replaced amino acids; catalyzes reaction of a transpepti-dirovaniye. In medicine attempts to use P. for treatment of diseases of connecting and cartilaginous fabrics (a palmar fibromatosis, a diskosis, an optokhiazmalny arachnoiditis, etc.), and also osteochondrosis become. Items apply in the meat industry to improvement of flavoring and nutritious qualities of meat and meat products, in the food industry — to clarification of beer, but also, to processing of skin, etc. In pilot medicobiological studies P. use during the studying of a structure of various proteins and peptides.
Items opened at the end of 19 century A. Wurtz and E. Bouchut, in 1937 it was received in a crystal look. This enzyme is the most studied representative of thiol proteinases (see. Peptide-hydrolase ).
Pier. the weight (weight) of P. apprx. 23 500, it Isoelectric point (see) is at pH 8,75.
The molecule P. consists of one polypeptide chain constructed of 212 amino-acid remains and is curtailed into the globule having almost spherical shape; it contains apprx. 20% and-siiraley and consists of two domains divided by a crack. In this crack the active center of enzyme is located, the SH group of the rest of cysteine-25 and imidazolny group of a histidine-159, and also asparagine-175 are a part to-rogo and asparaginic to - that is 158. The SH group, necessary for manifestation of enzymatic activity, easily is exposed to oxidation therefore manifestation of optimum activity of P. requires presence of activators — the recovering and metallsvyazyvayushchy agents, napr, mixes of cysteine and EDTA or one cysteine, glutathione, thioglycolic to - you, cyanide, Na 2 S 2 O 3 , NaBH 4 etc. Oxidizers, ions of heavy metals, and also the substances modifying SH groups suppress P. S activity ions of Hg 2+ papayas are formed by an inactive complex. In the presence of the recovering and metallsvyazyvayushchy agents this complex collapses and P.'s activity is completely recovered. The item is stable at pH 4,5 — 10,0, in more acid medium it is quickly inactivated; enzyme is steady in the concentrated solutions of urea, in 70% methanol, in the neutral environment is stable even at 70 °.
The item has wide substrate specificity. In synthetic substrates P. most quickly hydrolyzes the bonds formed by CO groups of the main amino acids. An optimum of pH for action of Item from 5,0 to 8,0.
Commercial drugs of the crude P. receive simple drying of natural latex of a melon tree. Along with P. are present at these drugs close to it on properties himopapain and peptidase A, to-rye differ from P. in the substrate specificity. Crystal P. is received from commercial drugs of enzyme by dopants deposition at pH 9,0 and the subsequent fractionation by ammonium sulfate and sodium chloride. Will crystallize P. from 0,02 M of solution of pH 6,5 cysteine at 4 °.
Bibliography: Mosolov V. V. Proteolytic enzymes, M., 1971; D of e n t h J. a. o. Papain, X-ray structure, in book: The enzymes, ed. by P. D. Boyer, v. 3, p. 484, N. Y. — L., 1971; Glazer A. N. a.S m i t h E. L. Papain and other piant sulf-hydryl proteolytic enzymes, ibid., p. 502.
L. A. Lokshina.