Thomas P D, Poznansky M J
Department of Physiology, University of Alberta, Edmonton, Canada.
Biochim Biophys Acta. 1989 Jan 16;978(1):85-90. doi: 10.1016/0005-2736(89)90502-6.
The effect of curvature on transbilayer lipid asymmetry in vesicles is investigated using vesicles of different sizes (30-140 nm) prepared by sonication and polycarbonate filter extrusion techniques. The transbilayer distributions of phosphatidylethanolamine and gangliosides are measured using 2,4,6-trinitrobenzenesulphonic acid and Clostridium perfringens neuraminidase as non-penetrating probes, respectively. The distribution of phosphatidylethanolamine in a phosphatidylcholine/phosphatidylethanolamine (4:1, molar ratio) system is more or less symmetric and curvature seems to have little effect. However, the distribution of gangliosides in a phosphatidylcholine/ganglioside (10:1, molar ratio) system is asymmetric in favour of the outer layer in smaller vesicles, the asymmetry disappearing as the degree of curvature decreases. In a phosphatidylcholine/phosphatidylethanolamine/ganglioside (8:2:1, molar ratio) system, both phosphatidylethanolamine and gangliosides distribute asymmetrically, indicating a composition-dependent asymmetric distribution of phosphatidylethanolamine. In this system asymmetry also increases with increasing curvature. The asymmetric distribution of gangliosides in vesicles of low curvature may be due to their long headgroup and larger headgroup surface area in accordance with the theoretical predictions of Israelachvili et al. (Biochim. Biophys. Acta 470 (1977) 185-201).
利用超声处理和聚碳酸酯滤膜挤压技术制备的不同尺寸（30 - 140纳米）的囊泡，研究了曲率对囊泡跨膜脂质不对称性的影响。分别使用2,4,6 - 三硝基苯磺酸和产气荚膜梭菌神经氨酸酶作为非穿透性探针，测量磷脂酰乙醇胺和神经节苷脂的跨膜分布。在磷脂酰胆碱/磷脂酰乙醇胺（摩尔比4:1）体系中，磷脂酰乙醇胺的分布或多或少是对称的，曲率似乎影响不大。然而，在磷脂酰胆碱/神经节苷脂（摩尔比10:1）体系中，神经节苷脂在较小囊泡中的分布是不对称的，有利于外层，随着曲率程度降低，这种不对称性消失。在磷脂酰胆碱/磷脂酰乙醇胺/神经节苷脂（摩尔比8:2:1）体系中，磷脂酰乙醇胺和神经节苷脂都呈不对称分布，表明磷脂酰乙醇胺的分布存在成分依赖性不对称。在该体系中，不对称性也随着曲率增加而增加。根据Israelachvili等人（《生物化学与生物物理学报》470 (1977) 185 - 201）的理论预测，低曲率囊泡中神经节苷脂的不对称分布可能是由于它们的长头部基团和较大的头部基团表面积。
