THE SEPARATION OF MAJOR COMPONENTS OF THE CASEIN OF BOVINE MILK BY ELECTROPHORESIS IN A DENSITY GRADIENT.

1. Zonal electrophoresis in a column stabilized by a density gradient has been applied to the small-scale fractionation of the proteins of the casein complex of cow's milk. 2. The alpha(s)- and beta-fractions from the milk of individual Ayrshire cows have been shown to behave as single homogeneous proteins on electrophoresis at two pH values in starch gels. 3. The alpha(s)-fraction has been found to be indistinguishable from alpha(s)-casein prepared by Ca(2+) fractionation of the same milk samples. 4. On the evidence of their electrophoretic behaviour in starch gels and their elementary analyses, alpha(1)- and alpha(s)-casein are concluded to be substantially the same protein.