Phospholipase A2: Action on Purified Phospholipids as Affected by Deoxycholate and Divalent Cations

Abstract

Phospholipase A2 preparations from a snake venom (Crotalus adamanteus) and from beef and human pancreas have been compared in identical reaction systems. With all of the substrates investigated the venom enzyme exhibited a higher specific activity in the presence of added sodium deoxycholate than in its absence. Under optimal conditions, the venom enzyme hydrolyzed phosphatidylcholine and phosphatidylethanolamine at equivalent rates, phosphatidylserine less well, and phosphatidylinositol more slowly still. Phosphatidylethanolamine was the preferred substrate for the pancreatic enzymes; although other phospholipids were hydrolyzed more rapidly in the presence of deoxycholate, its addition inhibited the conversion of this substrate to lysophosphatidylethanolamine.All three enzymes were stimulated by added Ca2+ ions whether phosphatidylcholine, phosphatidylethanolamine, or phosphatidylserine was employed as a substrate, the effect being quantitatively of greater significance with the reptilian as compared to the mammalian enzymes. Mg2+ ions could replace Ca2+ ions partially in some cases, especially with phosphatidylserine as substrate. Other divalent ions from the alkaline-earth and transition metal groups inhibited.The action of EDTA is complex; the results suggest that it has a direct inhibitory action on the enzymes.