Application of PhastSystem to the resolution of bovine milk proteins on urea-polyacrylamide gel electrophoresis.

Optimal conditions were established for alkaline urea-PAGE using modified precast, ultrathin gradient gels on the automated PhastSystem. Profiles of milk proteins showed that the caseins and whey proteins resolved extremely well. Major bands were observed for alpha s1-casein and beta-casein, and alpha s2-casein appeared as a well-resolved doublet. In contrast, kappa-casein separated from other caseins as a faint doublet, and purified kappa-casein appeared as one major and one minor band. Whey proteins (serum albumin, alpha-lactalbumin, beta-lactoglobulin) separated into broad bands resolved from each other and from the caseins. Partially (40%) dephosphorylated whole casein showed multiple bands for alpha s1-casein and beta-casein at different levels of phosphorylation. Separation of genetic phenotypes was observed for beta-lactoglobulin A and B; alpha s1-casein A, B, and C; and beta-casein A, B, and C. Electrophoretic patterns of milk proteins extracted from cheese samples varied among the different types of cheeses. Our modified procedure provides researchers with a rapid technique to separate both caseins and whey proteins on the same urea gel according to their charge to mass ratios.