PROPERTIES OF PHOSPHOLIPASE-A2 ISOLATED FROM RAT SERUM

Phospholipase A2 was extensively purified (1300- to 1400-fold) from rat serum using Sephadex G-100 chromatography. It eluted at a position corresponding to a molecular mass of about 15 kDa. This one purification step gave two bands on sodium dodecyl sulfate - polyacrylamide gel electrophoresis. The faster component had a molecular mass of 16 kDa and the slower band likely contained an aggregate of the faster component. Activity was associated with protein bands on nondenaturing gels. Enzyme activity was assessed using phosphatidylcholine or phosphatidylethanolamine labelled at sn position 2 with radioactive arachidonate. Phosphatidylethanolamine gave higher specific activities than phosphatidylcholine. The enzyme has an absolute requirement for Ca2+ and a pH optimum at 7.4. This pH optimum was more prominent for phosphatidylethanolamine. Activity was inhibited by oleate or arachidonate when phosphatidylcholine was used as substrate, but added free fatty acid did not significantly affect the hydrolysis of phosphatidylethanolamine. Addition of bovine serum albumin (fatty acid free) to assays increased the rate of release of arachidonate from phosphatidylcholine, but not from phosphatidylethanolamine. Phospholipase A2 is present in serum likely as a consequence of blood coagulation and may release fatty acids from cellular membranes following hemorrhage.