Membranes of Animal Cells: VI. THE GLYCOLIPIDS OF THE L CELL AND ITS SURFACE MEMBRANE

Abstract

Four glycolipid classes were isolated from mouse fibroblasts (L cells) and accounted for 0.7% of the total cell lipid. Ceramide lactoside was the only neutral glycolipid found and made up 20% of the total glycolipid. Mono- and disialoganglioside accounted for 38% of the cell glycolipid and hematosides containing N-acetylneuraminic and N-glycolylneuraminic acids made up an additional 42%. The L cell glycolipid pattern is similar to that of other fibroblasts but different than that of other extraneural tissues and of brain. Three of the four glycolipids contain predominantly short chain saturated fatty acids while the disialoganglioside contains 45% long chain fatty acids. Mild extraction of cells with 40% aqueous ethanol extracted approximately half of the cell lipid and selectively extracted two of the four glycolipids. Surface membranes of L cells were isolated by the fluorescein mercuric acetate method. Glycolipids accounted for 0.7% of the total membrane lipid. Only the hematosides and disialoganglioside could be found in the surface membranes. Ceramide lactoside and monosialoganglioside must be located in intracellular membranes. It is suggested that glycolipid content and the specific localization of glycolipids may be useful as criteria for the classification of membranes. Extraction of surface membranes with aqueous ethanol solubilized approximately 80% of the total membrane lipid including all of the hematosides. The disialoganglioside could be solubilized only after tryptic digestion of the membrane. Hydrophobic interactions between membrane proteins and specific lipids may be the primary stabilizing forces within the membrane matrix. Surface membrane glycolipids are resistant to neuraminidase activity and may be buried within the membrane matrix or are sterically inaccessible to neuraminidase.