Tumor lipids: Metabolic relationships derived from structural analyses of acyl, alkyl, and alk-1-enyl moieties of neutral glycerides and phosphoglycerides

Abstract

The composition of the hydrocarbon moieties of the 1-, 2-, and 3-positions of triglycerides and glyceryl ether diesters (GEDE) and of the 1- and 2-positions of diacyl and alkyl acyl phosphatidyl cholines (PC) and diacyl, alkyl acyl, and alk-1-enyl acyl phosphatidyl ethanolamines (PE) from Ehrlich ascites cells (EAC) were determined. The carbon number percentage distribution of triglycerides, GEDE, and the diglyceride-type acetates derived from each class of PC and PE was also determined by gas-liquid chromatography analysis of the intact lipids. The fatty acid compositions of the 1-, 2-, and 3-positions of the triglycerides are different and also differ from the composition of the corresponding positions of the GEDE, which are not the same. Both triglycerides and GEDE exhibit a 1-random-2-random-3-random type of distribution. The choline-contaning phosphatides consist of approximately 66% diacyl PC and 33% alkyl acyl PC. Ethanolamine-containing phosphatides are composed of 55% diacyl PE, 30% alkyl acyl PE, and 15% alk-1-enyl acyl PE. The carbon chain of the 1-position of each PC and PE class is predominantly saturated and the 2-position is dominated by polyunsaturated fatty acids. All PC and PE classes except the alk-1-enyl acyl PE show a l-random-2-random distribution. In EAC, randomly synthesized diglycerides are apparently used randomly for triglycerides and diacyl PC biosynthesis, and the biosynthesis of GEDE and alkyl acyl PC from an alkyl acyl intermediate also occurs without selectivity. In contrast, we have shown in a companion report that selectivity of diglycerides for the biosynthesis of triglycerides, PC, and PE occurs in rat liver. The similarities in composition at both the 1- and 2-positions between triglycerides and diacyl PC and between GEDE and alkyl acyl PC suggest a loss of acyl CoA: lysophosphatide acyl trausferase enzymes which are present in normal tissue. Metabolic relationships derived from structural analyses of acyl, alkyl, and alk-1-enyl moieties of glycerides and phosphoglycerides and from established pathways for acylation reaction led to the proposal of a metabolic pathway for the biosynthesis of lipids containing glyceryl ethers.