METABOLIC AND STRUCTURAL STUDIES OF POLYUNSATURATED LIPIDS IN CELL MEMBRANES

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The principal objective is to elucidate the structural and metabolic functions of polyunsaturated fatty acids or phospholipids with particular reference to their modulation by ethanol. Several approaches to this problem were taken including studies of cellular lipid composition, membrane asymmetry, fatty acid oxygenation and dietary supplementation. In particular, these studies focused on the major polyunsaturate of brain, docosahexaenoate (C22:6w3) and, to a lesser extent, on arachidonate (C20:4w6). We now report a new aspect of erythrocyte membrane structure; that is, phosphatidylethanolamine molecular species asymmetry. Polyunsaturated species containing arachidonate are preferentially localized on the cytoplasmic leaflet of the erythrocyte membrane. However, monoenoic species are more highly represented on the cell surface. Since alcohol causes a decline in polyunsaturated phospholipid species, we hypothesize a selective loss of membrane interior phospholipids. Conversely, dietary supplementation of omega-3 fatty acids led to increases in phospholipid species containing these acids that were localized to the membrane interior. Continued development of thermospray liquid chromatographic/mass spectrometric (LC/MS) techniques for phospholipid species has made possible a rapid, detailed and efficient analysis of all of the major lipid classes. Progress has been made in the quantification of phosphatidylcholines using deuterated internal standards. The biochemical characterization of the enzymatic oxygenation of 22:6w3 by rat brain homogenate was continued with respect to pH, enzyme inhibitors and various cofactors.