Human alpha S1-casein like protein: purification and N-terminal sequence determination.

Casein components of human milk are generally reported to belong to the beta- and kappa-groups. In this research human casein fraction was obtained from pooled mature milk, either by ultracentrifugation or by acid precipitation. In both cases a minor component with a slightly higher mobility in SDS-PAGE than beta-casein was identified. The protein was purified to homogeneity, the N-terminal sequence of the first 14 amino acid residues of this new human casein subunit shows a high degree of homology with the alpha s1-casein sequences from other species.