ACYLATION OF LYSOPHOSPHATIDYLSERINE BY RAT BRAIN MICROSOMES

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Abstract
The acylation of lysophosphatidylserine, prepared by snake venom digestion of phosphatidylserine, by rat brain microsomes is described. Acylation was monitored by spectrophotometric assay and by measuring the incorporation of radioactively labeled acyl CoA thioesters. Acylation was time dependent, showed an approximately linear response to enzyme concentration and had a pH optimum of 9.0. Maximum acylation was attained at a concentration of about 100 .mu.M for lysophosphatidylserine and about 40 .mu.M for acyl CoA thioesters. Positional distribution studies with [14C]oleoyl CoA and [14C]arachidonoyl CoA showed incorporation was predominantly at position -2, but with significant labeling at position -1, particularly with oleoyl CoA, possibly as a result of isomerization of the 1-acyl isomer of lysophosphatidylserine. Both saturated and unsaturated thioesters could serve as acyl group donors. Myristoyl CoA was considerably superior to palmitoyl CoA and stearoyl CoA, which were poor acyl group donors. Some selectivity was shown among the long chain unsaturated thioesters, linoleoyl, linolenoyl and arachidonoyl CoA being the most effective acylating agents. Although docosahexaenoic acid is a major unsaturated fatty acid in brain phosphatidylserine, its CoA ester was a relatively poor acyl group donor. Relative acylation rates remained essentially constant over a wide range of lysophosphatidylserine concentrations. Acyl transfer mechanisms are active in the brain for the regulation of the fatty acid profile of phosphatidylserine.

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