Bental M, Wilschut J, Scholma J, Nir S
Biochim Biophys Acta. 1987 Apr 9;898(2):239-47. doi: 10.1016/0005-2736(87)90043-5.
The effect of cholesterol on the Ca2+-induced aggregation and fusion of large unilamellar phosphatidylserine (PS) vesicles has been investigated. Mixing of aqueous vesicle contents was followed continuously with the Tb/dipicolinate assay, while the dissociation of pre-encapsulated Tb/dipicolinate complex was taken as a measure of the release of vesicle contents. Vesicles consisting of pure PS or PS/cholesterol mixtures at molar ratios of 4:1, 2:1 and 1:1 were employed at three different lipid concentrations, each at four different Ca2+ concentrations. The results could be well simulated in terms of a mass-action kinetic model, providing separately the rate constants of vesicle aggregation, c11, and of the fusion reaction itself, f11. In the analyses the possibility of deaggregation of aggregated vesicles was considered explicitly. Values of both c11 and f11 increase steeply with the Ca2+ concentration increasing from 2 to 5 mM. With increasing cholesterol content of the vesicles the value of c11 decreases, while the rate of the actual fusion reaction, f11, increases. Remarkably, the effect of cholesterol on both aggregation and fusion is quite moderate. The presence of cholesterol in the vesicle bilayer does not affect the leakage of vesicle contents during fusion.
研究了胆固醇对钙离子诱导的大单层磷脂酰丝氨酸（PS）囊泡聚集和融合的影响。通过Tb/二吡啶甲酸盐测定法持续跟踪水相囊泡内容物的混合情况，同时将预先包封的Tb/二吡啶甲酸盐复合物的解离作为囊泡内容物释放的量度。使用由纯PS或摩尔比为4:1、2:1和1:1的PS/胆固醇混合物组成的囊泡，在三种不同的脂质浓度下，每种浓度又在四种不同的钙离子浓度下进行实验。结果可以用质量作用动力学模型很好地模拟，分别给出囊泡聚集的速率常数c11和融合反应本身的速率常数f11。在分析中明确考虑了聚集囊泡解聚的可能性。随着钙离子浓度从2 mM增加到5 mM，c11和f11的值均急剧增加。随着囊泡中胆固醇含量的增加，c11的值降低，而实际融合反应的速率f11增加。值得注意的是，胆固醇对聚集和融合的影响相当温和。囊泡双层中胆固醇的存在不会影响融合过程中囊泡内容物的泄漏。
