ABSTRACT
The effect of the divalent cations Ca2+ and Mn2+ on the amidolytic activity of bovine plasma activated protein C and a limited chymotryptic digestion product, des-1-41-light chain activated protein C, which lacks all of the gamma-carboxyglutamic acid present in activated protein C, has been examined at 30 degrees C. In each case, the enzymic activities were dependent upon the presence of these cations, which exerted their effects primarily through influence on the kcat of the reaction. For both enzymes (E), the mechanism of the reaction was most consistent with a rapid equilibrium, random addition of substrate (S), and a single cation (A), with substrate hydrolysis occurring only with the ternary complex of S.E.A. The divalent cation site of importance was not associated with gamma-carboxyglutamic acid residues and was found to be independent of the monovalent cation sites, which also function to activate the amidolytic and esterolytic activities of these enzymes.
