SELECTIVE MODIFICATIONS OF THE PHOSPHOLIPID FATTY-ACID COMPOSITION IN HUMAN PLATELET MEMBRANES USING NONSPECIFIC AND SPECIFIC LIPID TRANSFER PROTEINS

In order to specifically modify the fatty acid composition of cell membrane phospholipids, we have developed an original method based on the transfer of pure phospholipid molecular species to membranes. Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) subclasses containing 18:2n-6 and 22:6n-3 at the sn-2 position were incorporated into human platelet membranes using the endogenous phosphatidylinositol-PC transfer protein (PI/PC-TP) and the phospholipid transfer protein from maize (L-TP), respectively, PI/PC-TP was shown to catalyze a strict exchange of phospholipids between platelet membranes and unilamellar vesicles containing 1,2-diacylglycerophosphocholine (diacyl-GPC; 16:0/18:2-GPC, or 16:0/22:6-GPC). The proportions of 18:2n-6 and 22:6n-3 in diacyl-GPC of platelet membranes were gradually increased from 10.7 to 16.9% and from 0.8 to 10.1%, respectively, whereas the PE and PI fatty acid compositions were not changed, The diacyl-GPC enrichment in 22:6n-3 and 18:2n-6 did not induce changes in membrane fluidity parameters measured by electron-spin resonance of 5- and 16-nitroxy stearic acids. Similarly, 18:2n-6 and 22:6n-3 esterified in 1,2-diacylglycerophosphoethanolamine (diacyl-GPE) have been incorporated in platelet membranes by an apparent exchange process under conditions where donor vesicles had a phospholipid composition equivalent to that of platelet membranes. The proportions of 18:2n-6 and 22:6n-3 were selectively and progressively increased from 6.0 to 21.2% and from 2.2 to 17.2%, respectively, in diacyl-GPE of platelet membranes, Thus, the L-TP- and PI/PC-TP-catalyzed enrichment can be used for studying the modulation of membrane biological activities by defined changes of fatty acid composition of specific phospholipid classes or subclasses. (C) 1995 Academic Press, Inc.