Simple Procedure for Isolation of Alphas-Casein

Starch gel electrophoretic patterns in 6 m urea – 1 m acetic acid buffer reveal that addition of a commercial polyphosphate (Quadrafos) to milk retards or reverses the migration of kappa-casein, indicating formation of a kappa-casein-polyphosphate complex. This reaction facilitates isolation of an alpha s -casein in a high state of purity. Milk is treated to contain 0.1% Quadrafos; made 3 m with respect to urea; and dialyzed against 3 m urea–0.1 m acetic acid solution until a precipitate forms. The precipitate is dissolved in 6 m urea–1 m acetic acid solution, centrifuged at room temperature for 2 hr at 105,000 g , and the clarified solution dialyzed against water. Gel electrophoresis shows that the protein is devoid of beta- and kappa-caseins, and has a molecular weight of 24,000±1% as determined by osmotic pressure measurements. Total and terminal amino acid residues are in good agreement with data in the literature.