628 Biochimica et Biophysica Acta, 598 (1980) 628--640 © Elsevier/North-Holland Biomedical Press BBA 78739 PHOSPHOLIPID AND CHOLESTEROL UPTAKE BY MYCOPLASMA CELLS AND MEMBRANES SHMUEL RAZIN, SHIRLEY KUTNER, HAVA EFRATI and SHLOMO ROTTEM Biomembrane Research Laboratory, The Hebrew University-l-ladassah Medical School, Jerusalem (Israel) (Received October 9th, 1979) Key words: Phospholipid uptake; Cholesterol uptake; Growth; (Mycoplasma) Summary The ability of growing mycoplasma cells and their isolated membranes to take up exogenous phospholipids was correlated with their ability to take up cholesterol. Horse serum or vesicles made of phosphatidylcholine and choles- terol served as lipid donors. Growing cells of five Mycoplasma species took up significant quantities of phosphatidylcholine and sphingomyelin as well as free and esterified cholesterol. In contrast, growing cells of three Acholeplasma species failed to take up any of the exogenous phospholipids, and only incorpo- rated low amounts of free cholesterol and no esterified cholesterol. Hence, the ability of mycoplasmas to take up large quantities of cholesterol appears to be correlated with an ability to take up exogenous phospholipids. Isolated mem- branes of Mycoplasma capricolum and Acholeplasma laidlawii took up lower amounts of cholesterol than did membranes of growing cells and did not take up phospholipids. Inhibition of M. capricolum growth decreased the ability of the cells to take up exogenous phospholipids and cholesterol. The possibility that the contact between the lipid donors and the membrane involves specific receptors best exposed in actively growing cells is discussed. Introduction Mycoplasmas offer several unique advantages for investigating the factors influencing the incorporation of exogenous lipids into biomembranes. The plasma membrane of these procaryotes is not covered by a cell wall, which enables it to interact directly with exogenous lipid donors. In addition, the majority of the mycoplasmas require exogenous cholesterol for growth and incorporate large quantities of it into the plasma membrane. The inability of