The vesicle-to-micelle transition of phosphatidylcholine vesicles induced by nonionic detergents: effects of sodium chloride, sucrose and urea

The vesicle-to-micelle transition of egg phosphatidylcholine LUVs induced b y octylglucoside was studied in buffers with 0-4 M sodium chloride, sucrose or urea. We used both light scattering and fluorescent probes to follow th e lipid-detergent complexes in these buffers. The vesicle-to-micelle transi tion process was fundamentally the same in each solute. However, the deterg ent-to-lipid ratio required for micelle formation shifted in ways that depe nded on the aqueous solute. The partitioning of octylglucoside between the vesicles and the aqueous phase was primarily determined by the change in it s critical micelle concentration (cmc) induced by each solute. Specifically , the cmc decreased in high salt and sucrose buffers but increased in high concentrations of urea. Cmc for two additional nonionic detergents, decyl- and dodecyl-maltoside, and three zwittergents (3-12, 3-14 and 3-16) were de termined as a function of concentration for each of the solutes. In all cas es NaCl and sucrose decreased the solubility of the detergents, whereas ure a increased their solubilities. The effects clearly depended on acyl chain length in urea-containing solutions, but this dependence was less clear wit h increasing NaCl and sucrose concentrations. The contributions of these so lutes to solubility and to interfacial interactions in the bilayers, pure a nd mixed micelles are considered. (C) 2000 Elsevier Science B.V. All rights reserved.