Tilcock C, Chin R, Veiro J, Cullis P, Fisher D
Department of Biochemistry, University of British Columbia, Vancouver, B.C. Canada.
Biochim Biophys Acta. 1989 Nov 17;986(1):167-71. doi: 10.1016/0005-2736(89)90287-3.
Unilamellar vesicles composed of phosphatidylcholine (PC) and either phosphatidic acid (PA) or phosphatidylglycerol (PG) partition to the upper poly(ethylene glycol) (PEG)-rich phase of a charge-sensitive 5%:5% (w/w) PEG 8000/Dextran T-500 phase system containing 10 mM sodium phosphate at pH 7, consistent with the vesicles bearing a net negative charge. When prepared in the presence of a pH gradient (interior acidic), PC/PA vesicles exhibit an increased partition to the top PEG-rich phase, consistent with a redistribution of the PA from the inner to the outer monolayer of the vesicle bilayer. Conversely, when prepared in the presence of a pH gradient (interior basic), PC/PG vesicles exhibit a decreased top-phase partition, consistent with a redistribution of the PG from the outer to the inner monolayer of the vesicle bilayer. Unilamellar vesicles composed of PC and stearylamine partition to the lower dextran-rich phase of a 5%:5% (w/w) PEG 8000/Dextran T-500 phase system containing 10 mM sodium phosphate at pH 8.5, consistent with the vesicles bearing a net positive charge. When prepared in the presence of a pH gradient (interior acidic), conditions under which the stearylamine is trapped on the inner monolayer of the bilayer, the vesicles now partition predominantly to the interface in a manner similar to vesicles composed of PC alone. These results demonstrate that partitioning in aqueous two-phase polymer systems is a sensitive method for monitoring the asymmetry of charged lipids in model membrane systems and also suggests that partitioning in charge-sensitive systems depends only on the physical nature of the exterior surface of the membrane.
由磷脂酰胆碱（PC）与磷脂酸（PA）或磷脂酰甘油（PG）组成的单层囊泡会分配到一个对电荷敏感的5%:5%（w/w）聚乙二醇8000/葡聚糖T - 500相系统的富含聚乙二醇（PEG）的上相，该系统含有10 mM磷酸钠，pH为7，这与囊泡带有净负电荷一致。当在存在pH梯度（内部呈酸性）的情况下制备时，PC/PA囊泡对顶部富含PEG相的分配增加，这与PA从囊泡双层的内层重新分布到外层一致。相反，当在存在pH梯度（内部呈碱性）的情况下制备时，PC/PG囊泡对顶部相的分配减少，这与PG从囊泡双层的外层重新分布到内层一致。由PC和硬脂胺组成的单层囊泡会分配到一个5%:5%（w/w）聚乙二醇8000/葡聚糖T - 500相系统的富含葡聚糖的下相，该系统含有10 mM磷酸钠，pH为8.5，这与囊泡带有净正电荷一致。当在存在pH梯度（内部呈酸性）的情况下制备时，即在硬脂胺被困在双层内层的条件下，囊泡现在主要以类似于仅由PC组成的囊泡的方式分配到界面处。这些结果表明，在水相双聚合物系统中的分配是监测模型膜系统中带电脂质不对称性的一种灵敏方法，并且还表明在对电荷敏感的系统中的分配仅取决于膜外表面的物理性质。
