Purification and Some of the Properties of αs-Casein and κ-Casein

αs-Casein and κ-casein have been freed of major contaminants, judged by starch-gel-urea electrophoresis. The αs-casein was prepared by a urea-sodium chloride procedure with a final precipitation of impurities by ethanol. κ-Casein was prepared by extraction of whole casein with urea-sulfuric acid supplemented with ethanol precipitation. Electrophoretic mobility, pH of minimal solubility salt-free (isoionic point), and with 0.1 m NaCl (isoelectric point), ultraviolet absorption, and interaction with calcium ions are reported.