Rottem S, Shinar D, Bittman R
Biochim Biophys Acta. 1981 Dec 21;649(3):572-80. doi: 10.1016/0005-2736(81)90161-9.
The exchange of cholesterol between [14C]cholesterol-labeled Mycoplasma gallisepticum cells and an excess of sonicated egg phosphatidylcholine/cholesterol vesicles (molar ratio of 0.9) was measured. More than 90% of the radioactive cholesterol underwent transfer from intact cells to the vesicles. The kinetics of the transfer was biphasic. About 50% of the radioactive cholesterol was exchanged with a half-time of about 4 h. The residual was exchanged at a slower rate with a half-time of about 9 h at 37 degrees C. Bovine serum albumin had a pronounced effect in enhancing both the fast and slow rates of cholesterol exchange, but did not affect the pool sizes significantly. The half-time for equilibration of the two pools in the presence of 2% albumin, calculated using a reversible two-pool method of analysis, was 6.2 h. The effect of albumin was also obtained with isolated membrane preparations and with cells treated with growth inhibitors, suggesting that this effect is independent of albumin preservation of cell viability. The rate enhancement of albumin was concentration dependent with maximal effects observed with greater than or equal to 2%, where the rates of exchange of both the rapidly and slowly exchanging pools were twice as fast. The mechanism by which albumin may affect the exchange rates is discussed.
测定了[14C]胆固醇标记的鸡毒支原体细胞与过量的超声处理的卵磷脂酰胆碱/胆固醇囊泡（摩尔比为0.9）之间的胆固醇交换。超过90%的放射性胆固醇从完整细胞转移到囊泡中。转移动力学呈双相性。约50%的放射性胆固醇在约4小时的半衰期内进行交换。残余部分在37℃下以较慢的速率交换，半衰期约为9小时。牛血清白蛋白对提高胆固醇交换的快速和慢速速率均有显著作用，但对池大小没有显著影响。使用可逆双池分析法计算，在存在2%白蛋白的情况下，两个池达到平衡的半衰期为6.2小时。在分离的膜制剂和用生长抑制剂处理的细胞中也观察到了白蛋白的作用，这表明这种作用与白蛋白对细胞活力的维持无关。白蛋白的速率增强是浓度依赖性的，当浓度大于或等于2%时观察到最大效应，此时快速和慢速交换池的交换速率都快了两倍。文中讨论了白蛋白可能影响交换速率的机制。
