Tumor lipids: Characterization of the lipids isolated from membranous material

Abstract

Membranous material was prepared from Ehrlich ascites carcinoma cells by zonal centrifugation. The distribution of fatty acids among the individual neutral lipid and phospholipid classes isolated from the membrane preparation was determined. Survey electron microscopy indicated that the preparations consisted of vesicles of rough surfaced endoplasmic reticulum, lysosomal-like structures, virus-like particles, few intact mitochondria, and unidentified amorphous material, in addition to plasma membranes. Lipids and proteins accounted for approximately one-third and two-thirds of the membranous material. Phospholipids accounted for two-thirds of the total lipids. The membranous material contained higher levels of free fatty acids, cholesterol, diacyl phosphatidyl choline, diacyl phosphatidyl ethanolamine, and lower levels of glyceryl ether diesters and cholesterol esters than whole cells. The fatty acid composition of all the lipid classes isolated from the membranous material, except phosphatidyl inositol and cholesterol esters, was similar to the fatty acid distribution of the corresponding classes obtained from whole cells. Cholesterol esters contained elevated levels of 16:1 and stearic acid accounted for 88% of phosphatidyl inositol fatty acids. Phosphatidyl choline and phosphatidyl ethanolamine isolated from the membranous preparations contained 1% or less alkyl acyl phosphatides, and plasmalogens were not detected. The lipids of whole Ehrlich ascites cells have been shown to contain high levels of ether-linked lipids, whereas these data indicate that alkyl and alk-1-enyl glyceryl ethers are virtually absent from membrane preparations of these cells. These results indicate that the ether-linked lipids are not distributed equally among all cell structures.