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Structure of Fully Hydrated Fluid Phase DMPC and DLPC Lipid Bilayers



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2626 Biophysical Journal Volume 88 April 2005 2626 2637 Structure of Fully Hydrated Fluid Phase DMPC and DLPC Lipid Bilayers Using X Ray Scattering from Oriented Multilamellar Arrays and from Unilamellar Vesicles Norbert Kuc erka Yufeng Liu Nanjun Chu Horia I Petrache z Stephanie Tristram Nagle y and John F Nagle y Physics and yBiological Sciences Departments Carnegie Mellon University Pittsburgh Pennsylvania and zLaboratory of Physical and Structural Biology The National Institute of Child Health and Human Development National Institutes of Health Bethesda Maryland ABSTRACT Quantitative structures of the fully hydrated uid phases of dimyristoylphosphatidylcholine DMPC and dilauroylphosphatidylcholine DLPC were obtained at 30 C Data for the relative form factors F qz for DMPC were obtained using a combination of four methods 1 Volumetric data provided F 0 2 Diffuse x ray scattering from oriented stacks of bilayers provided relative form factors jF qz j for high qz 0 22 qz 0 8 A 1 3 X ray scattering from extruded unilamellar vesicles with diameter 600 A provided jF qz j for low qz 0 1 qz 0 3 A 1 4 Previous measurements using a liquid crystallographic x ray method provided jF 2ph D j for h 1 and 2 for a range of nearly fully hydrated D spacings The data from method 4 overlap and validate the new unilamellar vesicles data for DMPC so method 4 is not required for DLPC or future studies We used hybrid electron density models to obtain structural results from these form factors Comparison of the model electron density pro les with that of gel phase DMPC provides areas per lipid A 60 6 6 0 5 A 2 for DMPC and 63 2 6 0 5 A 2 for DLPC Constraints on the model provided by volume measurements and component volumes obtained from simulations put the electron density pro les r z and the corresponding form factors F qz on absolute scales Various thicknesses such as the hydrophobic thickness and the steric thickness are obtained and compared to literature values INTRODUCTION The



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