THE HYDROLYSIS OF NATURAL PHOSPHATIDYLETHANOLAMINES BY PHOSPHOLIPASE-A2 FROM RAT SERUM - A DEGREE OF SELECTIVITY IS SHOWN FOR DOCOSAHEXAENOATE RELEASE

The selectivity of phospholipase A2 from serum was evaluated using radioassays and mass analyses of fatty acids liberated from phosphatidylcholine and phosphatidylethanolamine. These natural phospholipid substrates were labelled at the sn-2 position with radioactive oleate, linoleate and arachidonate. The rates of release of fatty acids were compared with their abundance at the sn-2 position of these phospholipid substrates. While there was little or no selectivity in the liberation of these fatty acids from phosphatidylcholine, there was some evidence for a preferential release of arachidonate with respect to linoleate from phosphatidylethanolamine. Mass analyses of free fatty acid products revealed that docosahexaenoate was consistently liberated at levels that exceeded its abundance at the sn-2 position of phosphatidylethanolamine. Three different, natural phosphatidylethanolamines with varying levels of docosahexaenoate showed a 1.2-1.8-fold enrichment of this polyunsaturate in the free fatty acid products compared with its abundance at the sn-2 position. This preference could also be shown when phosphatidylethanolamine was mixed with synthetic phosphatidylcholine as co-sonicated substrates. This preferential release of docosahexaenoate by serum phospholipase A2 is of considerable significance in the nervous system which is enriched in this polyunsaturate. The potential competition between liberated docosahexaenoate and arachidonate may be of fundamental importance in the response of brain to hemorrhage.