JOURNAL OF LIPOSOME RESEARCH, 9(2), 247-260 zyxw ( 1999) zyx LIPOSOMES CONTAINING SPHINGOMYELIN AND CHOLESTEROL: DETERGENT SOLUBILISATION AND INFRARED SPECTROSCOPIC STUDIES? Samir K. Patra, Alicia Alonso, Josh L. R. Arrondo, and FClix M. Goiii* Unidad de Biofkica (CSIC-UPV/EHU), and Departamento de Bioquimica, Universidad del Pais Vasco, Aptdo. 644, 48080 Bilbao, Spain ABSTRACT The solubilisation by Triton X-100 of large unilamellar vesicles con- sisting of pure egg sphingomyelin (T, = 39°C) or sphingomye1in:cholesterol mixtures has been tested at various temperatures. For pure sphingomyelin, solubilisation occurs most readily at temperatures just below T,. In general, egg sphingomyelin is solubilised by Triton X-100 more easily than egg phos- phatidylcholine. Mixtures of sphingomyelin and cholesterol are detergent- insoluble under most conditions. Infrared spectroscopy has been applied to explore the interactions of cholesterol and sphingomyelin at the level of the lipid-water interface. Moreover, various cholesterol analogues (cholestane, cholestanone, androstenol) have been used in parallel solubilisation experi- ments and IR observations. The results show that cholesterol modifies the con- formation (or H-bonding properties, or both) of the sphingomyelin polar head- group, both above and below T,. Moreover, both the hydroxyl group at C3 and the hydrocarbon chain at C17 of the steroid nucleus appear to be required for insolubility to be detected. Perturbation of the polar environment of the sphingomyelin : cholesterol bilayers by 3M urea makes them soluble in Triton ?This work is dedicated to the memory of Demetrios Papahadjopoulos. *Corresponding author: Fax: + 34-944648500; E-mail: zyxw gbpgourj@Zg. chum. zy 247 Copyright zyxwvut 0 1999 by Marcel Dekker, Inc. www.dekker.com Journal of Liposome Research Downloaded from informahealthcare.com by UPV University of Pais Vasco on 10/10/14 For personal use only.