Purification and characterization of human platelet phospholipase A 2which preferentially hydrolyzes an arachidonoyl residue

A phospholipase A 2with an arachidonoyl residue preference was purified about 11 700-fold from human platelet soluble fraction to near homogeneity. The purified phospholipase A 2exhibited 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 −7and 10 −6M free calcium ion. Thus, the 90-kDa phospholipase A 2is considered to be a novel enzyme, distinct from the 14-kDa one previously purified from human platelets. The 90-kDa phospholipase A 2may participate mainly in arachidonate metabolism of platelets.