College Park, Maryland      June 6 - 10 , 2004

WP6: Dynamics in Lecithin/Cholesterol Membranes by Deuterium Labeling

D. Worcester (Biology Division, University of Missouri, Columbia, MO 65211), J. Torbet (School of Medicine, University of Pennsylvania, Philadelphia, PA 19104), H. Kaiser (Research Reactor, University of Missouri, Columbia, MO 65211), E. Oldfield, C. Lea (Chemical & Life Sciences, 600 S. Matthews Ave., Urbana, IL 61801)

Dynamic properties of lecithin/cholesterol membranes were measured by deuterium labeling and neutron diffraction from multi-layers. Deuterium was introduced at specific molecular sites to provide a localized label for difference analysis. One hydrocabon chain of dimyristoyl-phosphatidylcholine was labeled at seven different methylene groups and at the terminal methyl group. The methyl groups of the lecithin choline were labeled and cholesterol was labeled with five deuterium near the hydroxyl group. B-values of the Debye-Waller factors were obtained by fitting difference structure factors in reciprocal space. Diffraction patterns with at least eight orders of Bragg diffraction were obtained for hydration ranging from 58% to nearly 100% relative humidity. Positions of the label were readily determined with uncertainty less than 1% of the repeat unit. The B-values were more difficult to determine and uncertainties were about 10%. The results show clear differences in the B-values of the different molecular groups. The cholesterol label had the smallest B-value, as expected for the rigid steroid ring. The hydrocarbon chain of dimyristoyl-phosphatidylcholine is well-ordered, with similar B-values along the chain. The results indicate that molecular packing is an important aspect of the preferential interaction of cholesterol with saturated lipids.

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