Characterization of lipovitellenin components, and their relation to low-density liproprotein structure

Abstract

When aqueous solutions of the LDF of egg yolk and its fractions LDF₁ and LDF₂ were extracted with ethyl ether, all yielded five derived components having sedimentation rates of about 4 S, 7 S, 13 S, 15 S and 17 S. The first three of these were isolated and had molecular weights of 2.9·10⁵, 11·10⁵ and 13·10⁵, and lipid contents of 50, 67 and 44%, respectively. These components were formed sequentially in the order 7 S → 4 S → 13 S and hence all contain the same proteins, although different combinations of polypeptide chains may be present. Apparently a reduction in lipid content below 50% causes an aggregation of 4-S particles to form 13 S and other rapidly sedimenting products. The sizes of the protein moieties, computed from the molecular weight and lipid content of the native fractions LDF₁ and LDF₂ and the derived products 7 S and 4 S, are in the order 8, 4, 2 and 1, respectively, with the smallest unit size estimated to be (1.7 ± 0.16) ·10⁵. Evidently the size of the protein moiety decreases stepwise as the lipid content decreases down to 4 S and this behavior, plus aggregation at low lipid contents, yields detectable and separable components in both the natural and derived from of these lipoproteins.