TERMINAL AMINO ACIDS OF EGG YOLK LIPOPROTEINS

Abstract

The N-terminal amino acids of the two lipovitellins and lipovitellenin of egg yolk have been determined. α-Lipovitellin and β-lipovitellin were separated by chromatography on hydroxyapatite but the lipovitellenin in the low-density fraction did not yield stable and reproducible chromatographic components. The major N-terminal amino acids recovered as dinitrophenyl derivatives from all three fractions were arginine and lysine. Further purification removed several minor components, but tyrosine and serine remained in vitellin, and alanine and serine in vitellenin. The principal C-terminal amino acid of vitellenin was glutamic acid. Arginine appeared to be the chief N-terminal residue but difficulty in purifying the water-soluble dinitrophenyl-amino acids led to highly variable yields; thus the total calculated amounts of terminal amino acids ranged from 9 to 35 micromoles per gram of protein. At least two polypeptide chains are indicated, with an average molecular weight less than the size of the total protein moiety of the parent lipoprotein. This is consistent with reported physical measurements in formic acid. The three lipoprotein fractions are indistinguishable on the basis of their terminal amino acids.