THE ACTIVITIES OF ACYL-COA-1-ACYL-LYSOPHOSPHOLIPID ACYLTRANSFERASE(S) IN HUMAN PLATELETS

The activities of acyl-CoA: 1-acyl-lysophospholipid acyltransferases (EC 2.3.1.23) have been studied in human platelet lysates by using endogenously formed [C-14]acyl-CoA from [C-14]fatty acid, ATP and CoA in the presence of 1-acyllysophosphatidyl-choline (lysoPC), -ethanolamine (lysoPE), -serine (lysoPS) or -inositol (lysoPI). Linoleic acid as fatty acid substrate had the highest affinity to acyl-CoA: I-acyl-lysophospholipid acyltransferase with lysoPC as variable substrate, followed by eicosapentaenoic acid (EPA) and arachidonic acid (AA). The activity at optimal conditions was 7.4, 7.3 and 7.2 nmol/min per 10(9) platelets with lysoPC as substrate, with linoleic acid, AA and EPA respectively. EPA and AA were incorporated into all lyso-forms. Linoleic acid was also incorporated into lysoPE at a high rate, but less into lysoPS and lysoPI. DHA was incorporated into lysoPC and lysoPE, but only slightly into lysoPI and lysoPS. Whereas incorporation of all fatty acids tested was maximal for lysoPC and lysoPI at 200 and 80 muM respectively, maximal incorporation needed over 500 muM for lysoPE and lysoPS. The optimal concentration for [C-14]fatty acid substrates was in the range 15-150 muM for all lysophospholipids. Competition experiments with equimolar concentrations of either lysoPC and lysoPI or lysoPE resulted in formation of [C-14]PC almost as if lysoPI or lysoPE were not added to the assay medium.