Enzymic Degradation of a Phosphopeptide Obtained by Trypsin Hydrolysis of alpha-Casein. A Partial Structural Formula.

Abstract

A tryptic [alpha]-case in phosphopeptide has been subjected to the action of pepsin, leucine aminopeptidase and carboxypeptidases. The pepsin hydrolysates are fractionated on Dowex 1-X2 columns (magnesium acetate gradient). Paper electrophoresis, amino-terminal group analysis and quantitative amino acid determination on resulting peptide fractions indicate that pepsin splits the phosphopeptide into four main peptide fragments. Partial sequences of these peptides are obtained, so that they can be placed in unique positions in the molecule. The seven phosphoamino acid residues are localized in the amino-terminal half of the peptide. Four of these can be arranged consecutively, while the others seem to be linked to different amino acid residues.