抄録
The effects of halides on the dipeptidyl and tripeptidyl carboxypeptidase activities of kininase II (angiotensin-converting enzyme, EC 3.4.15.1) purified from hog kidney were investigated. The dipeptidyl carboxypeptidase activity of the enzyme for bradykinin in the absence of halides was found to be buffer-dependent, and was decreased by the anions in potassium phosphate, N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (Hepes), Tris-H2SO4, Tris-H3PO4 and Trisacetate buffers with increasing concentration of these buffers (1-100mM) ; however, the activity was unaffected by borate-sodium carbonate buffer in this concentration range. When boratesodium carbonate buffer was used, F- functioned as an activator by raising V (2-fold) without modifying Km, while the other halides (Cl-, Br- and I-) hardly influenced V/Km (there were decreases of both V and Km), despite the fact that all the halides functioned as activators in various buffers by raising V (maximum 14-fold) without markedly affecting Km when angiotensin I was the substrate. The stimulatory effect of F- on bradykinin hydrolytic activity was maximum at 10mM, and it was reversed by various other anions (Cl-, Br-, I-, PO3-4, SO2-4, Hepes and CH3COO-). The V value of the enzyme for Gly-Phe-Ser-Pro-Phe (des-Arg9-bradykinin analogue), which is a substrate for the tripeptidyl carboxypeptidase activity of the enzyme (Biochim. Biophys. Acta, 662, 300, 1981), was enhanced by the addition of halides in the order Cl->Br->I->F-. On the other hand, the V value of the tripeptidyl carboxypeptidase activity of the enzyme for Gly-Pro-Ser-Pro-Phe, which has a proline residue at P1, like bradykinin, was enhanced to a lesser degree by halides and the maximal activity was obtained by the addition of 100mM F- (which resulted in a 2-fold increase of V).
