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

Goat κ-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 β-caseins. The goat κ-casein was identified by clotting with rennin, by specific changes in the electrophoretic pattern after rennin action, and by nonprecipitation with calcium ions. It stabilized goat αs-casein so that αs-casein was not precipitated with calcium ions. Polyacrylamide gel electrophoresis of goat κ-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 κ-casein was reduced with mercaptoethanol. Components with the mobilities of para-κ-casein were present in considerable amounts in some preparations of κ-casein.