Efrati H, Rottem S, Razin S
Biochim Biophys Acta. 1981 Mar 6;641(2):386-94. doi: 10.1016/0005-2736(81)90494-6.
Membranes of Mycoplasma species take up 2--4 times more exogenous cholesterol than membranes of Acholeplasma species. To test whether the lower cholesterol uptake capacity of Acholeplasma is due to the high glycolipid content of their membranes, the phospholipids of Acholeplasma laidlawii and Mycoplasma capricolum membranes were hydrolyzed by phospholipase A2. Digestion removed about 30% of the polar lipids of A. laidlawii, leaving the glycolipids and phospholglycolipids intact, and about 70% of the polar lipids of M. capricolum, the residue consisting mostly of sphingomyelin. Cholesterol uptake by the treated membranes from phosphatidylcholine/cholesterol vesicles decreased in rough proportion to the amount of polar lipid removed, indicating that the glycolipids in A. laidlawii membranes can participate in cholesterol uptake. Trypsin digestion of growing cells and isolated membranes of M. capricolum decreased cholesterol uptake by about one-half. Similar treatment of A. laidlawii cells and membranes had no effect on cholesterol uptake. These findings suggest the existence of protease-sensitive receptors on the cell surface of M. capricolum responsible for tighter contact with the cholesterol/phosphatidylcholine vesicles. It is proposed that the ability of Mycoplasma species to take up large quantities of exogenous cholesterol and phospholipids depends on the presence of protein receptors for cholesterol donors, receptors which are absent in Acholeplasma species.
支原体属的细胞膜摄取外源性胆固醇的量比无胆甾原体属的细胞膜多2至4倍。为了测试无胆甾原体较低的胆固醇摄取能力是否归因于其细胞膜中高含量的糖脂，用磷脂酶A2水解莱氏无胆甾原体和山羊支原体细胞膜中的磷脂。消化去除了约30%的莱氏无胆甾原体极性脂质，而糖脂和磷酸糖脂保持完整；消化去除了约70%的山羊支原体极性脂质，残余物主要由鞘磷脂组成。经处理的细胞膜从磷脂酰胆碱/胆固醇囊泡摄取胆固醇的量大致与去除的极性脂质的量成比例减少，这表明莱氏无胆甾原体细胞膜中的糖脂可参与胆固醇摄取。用胰蛋白酶消化生长中的山羊支原体细胞和分离的细胞膜，胆固醇摄取量降低约一半。对莱氏无胆甾原体细胞和细胞膜进行类似处理对胆固醇摄取没有影响。这些发现表明山羊支原体细胞表面存在蛋白酶敏感的受体，这些受体负责与胆固醇/磷脂酰胆碱囊泡更紧密地接触。有人提出，支原体属摄取大量外源性胆固醇和磷脂的能力取决于胆固醇供体蛋白受体的存在，而无胆甾原体属不存在这种受体。
