Purification and characterization of human platelet phospholipase A2 which preferentially hydrolyzes an arachidonoyl residue

Abstract

A phospholipase A₂ with an arachidonoyl residue preference was purified about 11 700‐fold from human platelet soluble fraction to near homogeneity. The purified phospholipase A₂ exhibited a molecular mass of about 90 kDa on SDS polycrylamide gel electrophoresis and hydrolyzed phospholipids with a arachidonoyl residue more effectively than those with a linoleoyl residue. The catalytic activity of the purified enzyme detected with phosphatidylcholine as a substrate increased sharply between 3 × 10⁻⁷ and 10⁻⁶ M free calcium ion. Thus, the 90‐kDa phospholipase A₂ is considered to be a novel enzyme, distinct from the 14‐kDa one previously purified from human platelets. The 90‐kDa phospholipase A₂ may participate mainly in arachidonate metabolism of platelets.