Possible involvement of 1-acyl-glycerophosphorylinositol acyltransferase in arachidonate enrichment of phosphatidylinositol in human platelets.
Microsomes isolated from human platelets synthesize phosphatidylinositol by the action of acyl-CoA: 1-acyl-sn-glycerol-3-phosphorylinositol(1-acyl-GPI) acyltransferase. The properties of 1-acyl-GPI acyltransferase were compared with those of 1-acyl-glycerophosphorylcholine (1-acyl-GPC) acyltransferase. Apparent Km values of 1-acyl-GPI and 1-acyl-GPC acyltransferases for the corresponding acyl acceptor (lysophospholipid) were 22 and 20 microM, respectively, in the presence of arachidonoyl-CoA as fatty acyl donor. However, the Km value (1.3 microM) of 1-acyl-GPI acyltransferase for arachidonoyl-CoA was much lower than that (5.0 microM) of 1-acyl-GPC acyltransferase. Under optimal conditions, the acylation rate of 1-acyl-GPI with arachidonoyl-CoA was 2-6 times higher than with oleoyl-CoA and linoleoyl-CoA, and was very low with saturated fatty acyl-CoAs. The acylation rates with various acyl-CoAs for 1-acyl-GPI were different from those for 1-acyl-GPC. These results suggest that the reacylation pathway of 1-acyl-GPI participates in the incorporation of arachidonic acid to phosphatidylinositol in platelet microsomes. Furthermore, there were no significant effects of thrombin-activation on acyl-CoA specificity for 1-acyl-GPI and 1-acyl-GPC acyltransferase in human platelets.
D000214:Acyl Coenzyme A / Q000097:blood; D000217:Acyltransferases / Q000097:blood*; D001095:Arachidonic Acids / Q000097:blood*; D001792:Blood Platelets / Q000201:enzymology*; D004789:Enzyme Activation; D005992:Glycerol-3-Phosphate O-Acyltransferase / Q000097:blood*; D006801:Humans; D008861:Microsomes / Q000201:enzymology*; D010716:Phosphatidylinositols / Q000097:blood*; D013347:Subcellular Fractions / Q000201:enzymology; D013917:Thrombin / Q000378:metabolism
D000214:Acyl Coenzyme A; D001095:Arachidonic Acids; D010716:Phosphatidylinositols; D000217:Acyltransferases; C038660:1-acylglycerophosphorylinositol acyltransferase; D005992:Glycerol-3-Phosphate O-Acyltransferase; D013917:Thrombin