title: Cholesteryl hemisuccinate exhibits pH sensitive polymorphic phase behavior.
abstract: Cholesteryl hemisuccinate (CHEMS) is an acidic cholesterol ester that self-assembles into bilayers in alkaline and neutral aqueous media and is commonly employed in mixtures with dioleoylphosphatidylethanolamine (DOPE) to form 'pH sensitive' fusogenic vesicles. We show here that CHEMS itself exhibits pH sensitive polymorphism. This is evident from the fusogenic properties of large unilamellar vesicles (LUV) composed of CHEMS and direct visualization employing freeze-fracture electron microscopy. Below pH 4.3, LUV composed of CHEMS undergo fusion as monitored by lipid mixing assays and freeze-fracture electron micrographs reveal the characteristic striated signature of H( parallel) phase lipid. It is suggested that the pH dependent phase preferences of CHEMS contribute to the pH sensitivity of LUV composed of mixtures of CHEMS and DOPE.
authors.affiliation: Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of British Columbia, 2146 Health Sciences Mall, Vancouver, B.C., Canada. ismail@interchange.ubc.ca
authors.forename: I M
authors.initials: IM
authors.lastname: Hafez
authors.forename: P R
authors.initials: PR
authors.lastname: Cullis
mesh_terms: D002788:Cholesterol Esters / Q000737:chemistry*; D005614:Freeze Fracturing; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008081:Liposomes; D008561:Membrane Fusion; D008854:Microscopy, Electron; D010714:Phosphatidylethanolamines / Q000737:chemistry; D014867:Water
chemical_list: D002788:Cholesterol Esters; D008081:Liposomes; D010714:Phosphatidylethanolamines; D014867:Water; C020888:1,2-dielaidoylphosphatidylethanolamine; C013440:cholesteryl succinate