title: Detection of surface charge-related properties in model membrane systems by aqueous two-phase partition.
abstract: 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.
authors.affiliation: Department of Biochemistry, University of British Columbia, Vancouver, B.C. Canada.
authors.forename: C
authors.initials: C
authors.lastname: Tilcock
authors.forename: R
authors.initials: R
authors.lastname: Chin
authors.forename: J
authors.initials: J
authors.lastname: Veiro
authors.forename: P
authors.initials: P
authors.lastname: Cullis
authors.forename: D
authors.initials: D
authors.lastname: Fisher
mesh_terms: D007700:Kinetics; D008081:Liposomes; D008744:Methylamines; D008962:Models, Theoretical; D010712:Phosphatidic Acids; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D011092:Polyethylene Glycols; D013499:Surface Properties; D013997:Time Factors
chemical_list: D008081:Liposomes; D008744:Methylamines; D010712:Phosphatidic Acids; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D011092:Polyethylene Glycols; C027451:methylamine