Studies of Casein. II. Moving Boundary Electrophoresis of Casein Fractions with Particular Reference to α-Casein

Abstract

A moving boundary electrophoretic study is made of acid casein, total milk protein, first-cycle casein, second-cycle casein-fractions P and S, α-casein (free of x-casein), and β-casein. Two acid-casein preparations are examined over the pH range 6.3 to 8.8 (I 0.02 and 0.1). The two preparations behave slightly differently from each other, but both show differences from that examined by Warner (1944). In veronal buffer, pH 8, the splitting of the " α peak " is observed only after prolonged electrophoresis. However, it occurs even at l per cent. concentration and in phosphate buffer of pH 6 to 7. An abnormal distribution of areas, similar to that attributed by Krecji, Jennings, and Smith (1941, 1942) and Warner (1944) to α-β interaction, is observed. The patterns of α-casein (free of x-casein) over the pH range 3-8 show no marked splitting. Preparations of previous workers showing this heterogeneity probably contain x-casein. The splitting of the a peak in acid casein is due, at least in part, to the α- and x-components and their state of aggregation. The patterns of the other fractions examined do not provide further unequivocal evidence of this. The detection of true heterogeneity is further complicated by other interaction effects. The composition of second-cycle casein-fraction S is also discussed.