Studies on plasma membranes. XXII. Fatty acid profiles of lipid classes in plasma membranes of rat and mouse livers and hepatomas.

Plasma membranes were isolated from rat and mouse livers, a transplanted rat hepatoma, two transplanted mouse hepatomas and spontaneous mouse hepatomas. Phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, sphingomyelin, lysophosphatidylcholine, free fatty acids and triglycerides were separated and their fatty acid profiles determined. The various lipid classes of rat and mouse liver plasma membranes each demonstrated more or less specific fatty acid profiles. The number of double bonds decreased in the order: phosphatidylserine greater than or equal to phosphatidylethanolamine greater than phosphatidylinositol greater than phosphatidylcholine greater than or equal to sphingomyelin and lysophosphatidylcholine. Small species differences were noted in most lipid classes. A marked sex difference was observed in sphingomyelin of mouse liver membranes but in none of the phospholipids of rat liver membranes. The increased cholesterol content of all hepatoma versus liver plasma membranes was accompanied by a decrease of fatty acyl poly-unsaturation in most lipid classes of the rat hepatoma but not of the mouse hepatoma membranes. The fatty acid profiles of the mouse hepatoma membranes deviated much less from those of mouse liver than did the pattern of rat hepatoma versus rat liver. The results were discussed in relation to lipid fluidity of which fatty acyl unsaturation and cholesterol are the main parameters.