Identification of the κ-Casein Among the Components of Whole Goat Casein

Goat ,-casein in the reduced state, probably the natural state, has a mobility on acrylamide gel electrophoresis at pH 9, very close to that of the fi-easeins. The goat K-casein was identified by clotting with rennin, by specific changes in the electrophoretic pattern after rennin action, and by nonpreeipitation with calcium ions. It stabilized goat a,-casein so that a~-casein was not precipitated with calcium ions. PolyaczTlamide gel electrophoresis of goat K-casein in some cases gave a single band (together with identifiable contaminants), and, in other cases, gave a multiplicity of slower-moving bands. In all cases only a single major band was observed when the ~-casein was reduced with mereaptoethanol. Components with the mobilities of para-Kcasein were present in considerable amounts in some preparations of ~-casein.