Tumor lipids: Structural analyses of the phospholipids

The distribution of fatty acids esterified at the 1- and 2-positions of phosphatidyl serine (PS), phosphatidyl inositol (PI), and diphosphatidyl glycerol (DPG), and the fatty acid composition of sphingomyelins and ceramides isolated from Ehrlich ascites cells were determined. Diglycerides derived from PS, PI, and DPG by phospholipase C hydrolysis were also analyzed intact as acetate derivatives. Alkyl and alk-1-enyl glyceryl ethers were absent from PS, PI, and DPG, or present in only trace amounts. Predominately stearic acid was esterified at the 1-position of PS and PI. Stearic, 18:1, and 18:2 acids accounted for 34, 25, and 25% of the acids esterified at the 2-position of PS, whereas two-thirds of the 2-position acids of PI was 20:4. Both the 1- and 2-positions of DPG were dominated by 18:2 acid. More than 75% of the DPG was resistant to phospholipase C hydrolysis. The distribution of diglyceride species was different for each phosphatide. Sphingomyelin and ceramide fatty acids obtained from this neoplasm contained 9% of a C 24 dienoic acid, which is absent from sphingomyelin of normal tissue, or present in only trace amounts. The acid was identified as Δ 15, Δ 18-tetracosadienoic acid.