Kinetic parameters of lysophospholipid acyltransferase systems in diet-induced modifications of platelet phospholipid acyl chains.

Abstract

Competitive effectiveness and relative Km values of polyunsaturated fatty acids were determined in the acyl-CoA : lysophospholipid acyltransferase systems in platelet membranes. Some CoA esters of fatty acids such as 18 : 2n-6 (linoleic), 18 : 3n-3(α-linolenic), 18 : 3n-6, 20 : 3n-6 (dihomo-γ-linolenic) and 20 : 5n-3 (eicosapentaenoic) were found in vitro to be relatively good competitive inhibitors of arachidonate (20 : 4n-6) incorporation into phosphatidylcholine, while in the acylation of lysophosphatidylinositol, 18 : 2n-6, 20 : 2n-6, 20 : 3n-6, 20 : 5n-3 and 22 : 4n-6 were relatively good inhibitors. When vegetable oil-supplemented diets rich in 18 : 2n-6 or 18 : 3n-3 were fed to rats, these fatty acids were converted to highly unsaturated fatty acids such as 20 : 4n-6 and 20 : 5n-3, and were esterified to phospholipids in platelets. The kinetic parameters determined in vitro were useful in predicting grossly the relative abundance of eicosanoid precursors (20 : 4n-6 and 20 : 5n-3), but not that of 18-carbon polyunsaturated fatty acids. It was found that arachidonate was conserved but n-3 fatty acids were excluded relatively more strictly in phosphatidylinositol than in phosphatidylcholine in platelets of rats on diets containing different proportions of 18 : 2n-6 and 18 : 3n-3.