Preparation and amino acid sequence of human κ‐casein

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Abstract
Human κ-casein was prepared from whole casein by successive hydroxyapatite and thiol-Sepharose chromatographies. The primary structure of its 99-residue N-terminal fragment has been determined by sequencing peptides obtained by tryptic and chymotryptic digestions of the whole protein. This fragment overlaps the known sequence of the 65-residue C-terminal fragment. The 158-residue sequence of human κ-casein was compared to those of goat, ewe, cow and rat κ-caseins. Only 22% of the residues are identical in homologous positions. The rate of divergence of the 93-residue N-terminal segment (para-κ-casein) appears to be higher than that of the rest of the molecule.