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Simple Procedure for Isolation of Alpha_s-Casein¹

Carnation Research Laboratory, Van Nuys, California

ABSTRACT

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.

¹ Presented at the Sixtieth Annual Meeting of the American Dairy Science Association, Lexington, Kentucky (1965). J. Dairy Sci., 48:780.