Liquid diffraction analysis of sarcoplasmic reticulum. II. Solvent electron contrast variation.

Intensities of x-ray scattering from rabbit muscle sarcoplasmic reticulum membrane have been measured over the range of s = 0.05-0.25, at solvent densities varying between p0 = 0.335 and 0.389 electrons/A3. Analysis of the results shows agreement with the elements of structure deduced earlier by a different technique, based on the variation of the lipid-protein concentration ratio. In addition, the present work extends the analysis to allow isolation of the lipid contribution to the total scattering, from which a profile of the lipid electron density normal to the membrane face is evaluated. The scattering arising from electron correlations within the plane of the bilayer has also been identified.