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

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.