Small‐angle X‐ray scattering of human serum high‐density lipoproteins

Small‐angle x‐ray scattering (SAXRS) studies of the human serum high‐density lipoprotein HDL 2 indicate a symmetrical particle with a radius of gyration Rg = 46 Å. The positions and intensities of subsidiary maxima in the scattering curves are not consistent with those of a uniformly electron dense sphere. Scattering curves calculated for spheres with a step‐model radial electron density distribution, show good agreement with the experimental scattering curve for HDL 2 only for specific values of the step function used. The dimensions obtained for the electron‐deficient core and electron‐rich shell model are quantitatively consistent with a predominantly surface location for the HDL 2 protein and phospholipid head groups, the more hydrocarbon species being located in the interior of the particle.