Evidence for Lipid/Cholesterol Ordering in Model Lipid Membranes

¹ Intel Corporation
² The University of Chicago
³ Los Alamos National Laboratory
⁴ University of Copenhagen

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

Submitted on March 15, 2006
Revised on March 20, 2006
Accepted on 4 April 2006

	Abstract

It has been postulated that for a binary mixture of phospholipid and cholesterol, phospholipid/cholesterol complexes are formed at a particular stoichiometry. Using grazing incidence X-ray diffraction techniques, the existence of such complexes has been confirmed. Scattering features consistent with the existence of lipid/cholesterol complexes persist to high surface pressures even though fluorescence microscopy (FM) suggests a homogeneously fluid phase. Contrary to pure phospholipid and cholesterol systems, the resulting lattice spacing, integrated scattering intensity and coherence lengths of these complexes are almost independent of surface pressure. Furthermore, the single peak observed in these mixed systems is very broad, suggesting that the extent of order for a single scattering structure only persists over a few molecules. This observation is consistent with these complexes being dynamic structures.

Key Words: Condensed complexes, Grazing incidence X-ray diffraction, Langmuir trough, Lipid rafts, Phospholipid monolayers

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