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

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Abstract
NaCl stimulated the adenylate cyclase activities of human and rabbit platelet particulate fractions prepared in the presence of ethylene glycol bis(β‐aminoethyl ether)‐N,N,N′,N′‐tetraacetate, but inhibited the activities of particulate fractions proteolysed by endogenous Ca2+‐activated protease or treatment with α‐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).