Cholesteryl hemisuccinate exhibits pH sensitive polymorphic phase behavior

Cholesteryl hemisuccinate (CHEMS) is an acidic cholesterol ester that self- assembles into bilayers in alkaline and neutral aqueous media and is common ly employed in mixtures with dioleoylphosphatidylethanolamine (DOPE) to for m 'pH sensitive' fusogenic vesicles. We show here that CHEMS itself exhibit s pH sensitive polymorphism. This is evident from the fusogenic properties of large unilamellar vesicles (LW) composed of CHEMS and direct visualizati on employing freeze-fracture electron microscopy. Below pH 4.3, LUV compose d of CHEMS undergo fusion as monitored by lipid mixing assays and freeze-fr acture electron micrographs reveal the characteristic striated signature of H-parallel to phase lipid. It is suggested that the pH dependent phase pre ferences of CHEMS contribute to the pH sensitivity of LUV composed of mixtu res of CHEMS and DOPE. (C) 2000 Elsevier Science B.V. All rights reserved.