Effects of proteolysis on the actions of monovalent cations and 1-O-octadecyl-2-O-acetyl-sn-glyceryl-3-phosphorylcholine on platelet adenylate cyclase

NaCl stimulated the adenylate cyclase activities of human and rabbit platelet particulate fractions prepared in the presence of ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N',-tetraacetate, but inhibited the activities of particulate fractions proteolysed by endogenous Ca2+-activated protease or treatment with alpha-chymotrypsin. Studies with other monovalent cations showed that LiCl had weak effects similar to those of NaCl, whereas KCl inhibited the enzyme in both proteolysed and non-proteolysed preparations. The results suggest that NaCl exerts stimulatory and inhibitory effects through different sites. NaCl potentiated and proteolysis greatly reduced the inhibition of platelet adenylate cyclase by 1-O-octadecyl-2-O-acetyl-sn-glyceryl-3-phosphorylcholine (platelet-activating factor).