Lipid–protein interactions in abnormal egg yolk: a comparison of the major lipoprotein fractions from normal eggs and from the eggs of hens fed methyl sterculate

To help explain the known differences in texture and appearance between yolks of normal eggs and of eggs from hens whose diet contains cyclopropenoid compounds such as methyl sterculate, ultra-centrifuge patterns of solutions of the two sorts of yolk have been examined and physical and chemical properties of some of their macromolecular constituents have been compared.Abnormal yolk sedimented in 0.16 M sodium chloride, but it resembled normal yolk in that a major lipoprotein fraction floated in 1.0 M sodium chloride. This abnormal lipoprotein had a lower partial specific volume and flotation coefficient, and gave solutions with a higher viscosity, than the corresponding normal fraction. It had a higher protein content than normal, and its amino acid composition was slightly different, suggesting a different proportion of the constituent apoproteins. The abnormal lipoprotein contained slightly less of a new protein isolated because it remained soluble in a chloroform–methanol mixture. The amino acid composition of this protein differed from that of other yolk proteins. In particular, it contained very little histidine.In the abnormal lipoproteins, combination of protein and lipid appears to be such that strong interactions are possible between ngighboring lipoprotein particles in solution. In whole abnormal yolk, some of the livetins may interact with other yolk constituents thus contributing to the high viscosity. A higher proportion of saturated fatty acid residues in the lipids of abnormal yolk is the only factor so far correlated with the unusual interactions between lipid and protein in this yolk.