SYNTHESIS AND TURNOVER OF MEMBRANE PROTEIN AND LIPID IN MYCOPLASMA LAIDLAWII

The relatioship of lipid to protein synthesis in Mycoplasma laidlawii membranes was studied in heavy suspensions of the organisms in complex or partially defined media. Under the test conditions used the organisms did not multiply, and the amount of total cell protein remained constant. Lipid synthesis was measured by the incorporation of [3H]oleic acid into membrane lipids, while protein synthesis was measured by the incorporation of l-[14C]phenylalanine into membrane proteins. Though the ability of the cells to synthesize both membrane proteins and lipids declined steeply with age their protein-synthesizing ability was impaired at a much earlier stage. When membrane protein synthesis was arrested by treating the cells with chloramphenicol, the membrane lipid synthesis was not affected, so that the cell membranes formed had a density of 1.158 g/cm3 as against 1.170 g/cm3 for untreated cell membranes. The total membrane proteins labeled with l-[14C]phenylalanine turned over at a relatively high rate, having a half life of approx. 3 h. Turnover of the total membrane lipids labeled with [3H]oleic acid became apparent only after a lag period of several hours after the beginning of the chase. It was thus found that in M. laidlawii membrane lipid synthesis can be uncoupled from the synthesis of the membrane protein, so that the two processes are not necessarily synchronized. The possibility of varying the lipid to protein ratio in biological membranes without affecting their function is discussed. © 1969.