CARBOXYPEPTIDASE OF STREPTOMYCES-GRISEUS - IMPLICATIONS OF ITS CHARACTERISTICS

Carboxypeptidase from Streptomyces griseus has been isolated by use of a new, highly efficient affinity chromatographic procedure. The enzyme isolated in this manner consists of a single polypeptide chain with a molecular weight of 41 200. It is reversibly inhibited by o-phenanthroline and other metal chelators and contains 1 g-atom of zinc/mol. The absorption and magnetic circular dichroic spectra of the cobalt-substituted enzyme are virtually identical with those previously observed for bovine carboxypeptidase A. Moreover, chemical modification studies suggest the importance of ty-rosyl, arginyl, and glutamyl residues for catalytic activity, all of which have been demonstrated to be essential for the activity of bovine carboxypeptidase A. Importantly, the S. griseus carboxypeptidase exhibits unique properties not previously observed in other zinc carboxypeptidases. It contains 2 g-atoms of tightly bound calcium which appears to function in protein stabilization in concert with two disulfide bridges. In marked contrast to any of the metallocarboxypeptidases known presently, the S. griseus enzyme hydrolyzes C-terminal basic peptide substrates and their exact ester analogues with kinetic parameters comparable to those of the corresponding neutral C-terminal substrates. These properties of this bacterial enzyme, combined with its close mechanistic similarity to bovine carboxypeptidase A, suggest that it may be the postulated but yet to be identified intermediate between endo-peptidases and the carboxypeptidases. © 1979, American Chemical Society. All rights reserved.