Sadana T, Sanyal S N, Majumdar S, Dhall K, Chakravarti R N
Biochem Cell Biol. 1986 Jun;64(6):575-82. doi: 10.1139/o86-080.
[14C]Cholesterol movement between egg phosphatidylcholine-cholesterol lipid vesicles and vesicles prepared from monkey small intestinal brush border membrane (BBMV) was studied in physiological buffer at 37 degrees C. The rate of cholesterol transfer from sonicated unilamellar vesicles (ULV) to BBMV follows apparently first-order kinetics. Intermembrane cholesterol movement was strikingly similar in both the directions. However, from BBMV to ULV, the transfer rate was three times faster than that of ULV to brush border membrane (BBM). Similarity in the rate constant was observed when cholesterol transfer was studied using either large multilamellar lipid vesicles or ULV as the donor and BBMV as the acceptor membrane. Rate constant was also the same when the acceptor membrane used was either intact BBMV or ULV prepared from BBM lipids. The rate of transfer of label was not affected even when the acceptor vesicle concentration was increased over fivefold, indicating the first-order nature of the reaction. Transfer of cholesterol from ULV to BBMV was accelerated by the presence of acetone, dimethyl sulfoxide (DMSO), deoxycholate, and papain. Partially purified nonspecific lipid-exchange protein increased the rate of cholesterol transfer by about threefold. Reduction in BBM cholesterol and phospholipid content was noted by DMSO, acetone, and deoxycholate, while papain caused a small depletion of membrane protein. Cholesterol transfer is temperature dependent with an activation energy of 31 kJ X mol-1, which is almost identical in the presence or absence of nonspecific lipid-exchange protein. The molecular mechanism of intermembrane cholesterol movement is discussed in view of the kinetic data obtained.
在37℃的生理缓冲液中，研究了[14C]胆固醇在鸡蛋磷脂酰胆碱 - 胆固醇脂质囊泡与由猴小肠刷状缘膜（BBMV）制备的囊泡之间的移动情况。胆固醇从超声处理的单层囊泡（ULV）转移至BBMV的速率显然遵循一级动力学。两个方向上膜间胆固醇的移动都极为相似。然而，从BBMV到ULV的转移速率比从ULV到刷状缘膜（BBM）的转移速率快三倍。当使用大型多层脂质囊泡或ULV作为供体且BBMV作为受体膜来研究胆固醇转移时，观察到速率常数具有相似性。当使用完整的BBMV或由BBM脂质制备的ULV作为受体膜时，速率常数也相同。即使受体囊泡浓度增加超过五倍，标记物的转移速率也不受影响，这表明该反应具有一级反应的性质。丙酮、二甲基亚砜（DMSO）、脱氧胆酸盐和木瓜蛋白酶的存在会加速胆固醇从ULV向BBMV的转移。部分纯化的非特异性脂质交换蛋白使胆固醇转移速率提高了约三倍。DMSO、丙酮和脱氧胆酸盐可使BBM中的胆固醇和磷脂含量降低，而木瓜蛋白酶会导致膜蛋白少量消耗。胆固醇转移与温度有关，其活化能为31 kJ·mol-1，无论是否存在非特异性脂质交换蛋白，该活化能几乎相同。根据所获得的动力学数据，对膜间胆固醇移动的分子机制进行了讨论。
