SUMMARY: The cell membrane of was isolated by either ultrasonic or French press treatment of intact cells. The membrane fraction contained all of the cellular lipids, but only one-third of cellular proteins and had a density of 1.14 g ml. The soluble fraction contained the NADH dehydrogenase activity of the cells, as well as a protein with an apparent molecular mass of 55 kDa that was phosphorylated in the presence of ATP. Lipid analyses of membranes revealed that membrane lipid could be labelled by radioactive glycerol, oleate and to a much higher extent by palmitate but not by acetic acid. The membrane lipid fraction was composed of 54% neutral and 46% polar lipid. The major constituents of the neutral lipid fraction were free fatty acid, free cholesterol and cholesterol esters (45,25 and 20%, respectively, of total neutral lipid fraction). The free cholesterol count was 13% (w/w) of total membrane lipids with a cholesterol:phospholipid molar ratio of about 0.9. Among the polar lipids, both phospho-and glycolipids were detected. The phospholipid fraction consisted of a major phosphatidylglycerol (63% of total phospholipids), plus exogenous phosphatidyl-choline and sphingomyelin incorporated in an unchanged form from the growth medium. The glycolipid fraction was dominated by a single glycolipid (90% of total glycolipids) that was preferentially labelled by palmitic acid and showed a very high saturated:unsaturated fatty acids ratio.


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