STATES OF AGGREGATION AND PHASE-TRANSFORMATIONS IN MIXTURES OF PHOSPHATIDYLCHOLINE AND OCTYL GLUCOSIDE
STATES OF AGGREGATION AND PHASE-TRANSFORMATIONS IN MIXTURES OF PHOSPHATIDYLCHOLINE AND OCTYL GLUCOSIDE
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DOI：
10.1021/bi00471a012
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发表时间：
1990-05-15
期刊：
影响因子：
2.9
通讯作者：
LICHTENBERG, D
中科院分区：
文献类型：
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作者：
ALMOG, S;LITMAN, BJ;LICHTENBERG, D
将不同浓度的非离子去污剂辛基糖苷（OG）与通过超声处理制备的卵磷脂酰胆碱（PC）的小单层囊泡（SUV）混合的结果取决于混合聚集体中OG和PC之间的比率。当该摩尔比（Re）低于1.4时，洗涤剂在PC囊泡和水性介质之间分配，分配系数为K = 0.033 mM-1。由于将OG引入双层中，囊泡的尺寸增大。 所得囊泡的平均直径是Re的递增函数，并且与总PC浓度无关。在暴露于OG之前用高分子量葡聚糖装载囊泡的实验表明，负责尺寸增长的机制涉及脂质转移而不是融合。Re值在1.4-3.2范围内的混合物分离成两个宏观相：下相是透明的，但非常粘稠。它含有恒定的OG和PC浓度，其特征在于Re值为3.2，与整个分散体的组成无关。上相含有不同浓度的OG和PC的囊泡，但常数Re为1.4。当接近每PC分子1.4个OG分子的饱和水平时，水性介质中OG单体的浓度达到16.6 ± 1的值。0.3 mM，其为含脂质培养基中OG的表观cmc。OG-PC混合胶束含有至少3.2个OG分子/PC分子。在Re = 3.2时，混合胶束的短轴约为2 nm，长轴约为25 nm，呈扁椭圆形。此时混合胶束的表面积刚好足以使它们转化为半径为12 nm的最小可能球形囊泡。在Re值高于3.2时，混合胶束的长轴随着Re的增加而变小，而在Re值低于3.2时，胶束将随着Re的降低而非常迅速地生长。这可以解释在Re = 3.2以下发生的部分囊泡闭合。
The result of mixing varying concentrations of the nonionic detergent octyl glycoside (OG) with small unilamellar vesicles (SUV) of egg phosphatidylcholine (PC) made by sonication depends on the ratio between OG and PC in the mixed aggregates. When this molar ratio (Re) is lower than 1.4, the detergent partitions between the PC vesicles and the aqueous medium with a partition coefficient of K = 0.033 mM-1. As a consequence of introduction of OG into the bilayers, the vesicles grow in size. The resultant vesicles have a mean diameter that is an increasing function of Re and is independent of the total PC concentration. Experiments in which the vesicles were loaded with high molecular weight dextran prior to being exposed to OG suggest that the mechanism responsible for the size growth involves lipid transfer rather than fusion. Mixtures with Re values within the range of 1.4-3.2 separate into two macroscopic phases: The lower phase is clear but very viscous. It contains constant OG and PC concentrations and is characterized by an Re value of 3.2, independent of the composition of the whole dispersion. The upper phase contains vesicles of varying concentrations of OG and PC, but a constant Re of 1.4. When the saturation level of 1.4 OG molecules per PC molecule is approached, the concentration of OG monomers in the aqueous medium reaches the value of 16.6 .+-. 0.3 mM, which is the apparent cmc of OG in the lipid-containing medium. OG-PC mixed micelles contain at least 3.2 OG molecules per PC molecule. The mixed micelles present at Re = 3.2 apparently have the shape of oblate ellipsoids with a minor axis of about 2 nm and two major axes of about 25 nm. The surface area of the mixed micelles at this point is just sufficient for them to undergo conversion into the smallest possible spherical vesicles of a radius of 12 nm. At Re values above 3.2, the major axis of the mixed micelles become smaller as Re increases, while at values of Re below 3.2 the micelles would have been expected to grow very rapidly with decreasing Re. This may explain the partial vesicle closure occurring below Re = 3.2.