Complexes in Ternary Cholesterol-Phospholipid Mixtures

¹ Stanford University

^* To whom correspondence should be addressed. E-mail: harden{at}stanford.edu.

Submitted on December 29, 2004
Revised on January 25, 2005
Accepted on 1 February 2005

	Abstract

ABSTRACT Recent work by Veatch and Keller has described liquid-liquid immiscibility in giant unilamellar vesicles composed of ternary mixtures of cholesterol, dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC). (2003, Biophys. J., 85:3074-3083). Significantly, they do not observe immiscibility in any of the three corresponding binary mixtures under the same conditions. It is shown here that this unexpected result can be accounted for by the formation of a complex between cholesterol and DPPC. The complex is miscible with DPPC and cholesterol, and immiscible with DOPC. A simple, idealized thermodynamic treatment of this model leads to theoretical ternary phase diagrams that are similar to the experimental diagram reported by Veatch and Keller. The model also accounts for significant qualitative features of the deuterium NMR spectra of these mixtures in bilayers.

Key Words: bilayer membranes, cholesterol, condensed complexes, deuterium NMR, phase diagrams

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