Phospholipid unsaturation and plasma membrane organization.

A comparison has been made between the unsaturation of plasma-membrane phospholipids,present in the human erythrocyte, rat liver, mouse liver and a rapidly growing rat hepatoma. Of the double bonds present in the hydrocarbon chains of the membrane phospholipids,onethird is contributed by sphingomyelin plus phosphatidyl choline and the remainder by phosphatidyl serine, ethanolamine and inositol. Assuming that the phospholipids are asymmetrically distributed in the two leaflets of the bilayer in general, the consequences of this asymmetry in combination with cholesterol content and fatty acid distribution on plasma membrane organization and function are discussed. It is suggested, that the organizational disposition of plasma membrane components other than phospholipids is at least related if not dependent upon the latter's asymmetric distribution in the bilayer.