Analysis of casein using two-dimensional electrophoresis, western blot, and computer imaging

Casein from milk of 20 mothers, 8 weeks postpartum, was analyzed using 2-dimensional electrophoresis. The casein micelle under 2-D denaturing conditions gives approximately 15 major spots. Beta-Casein, kappa-casein, para-kappa-casein, and casein peptides can be tentatively identified by molecular size, isoelectric point, and spot shape characteristics. All spots are not present in all samples. Two spots thought to represent different phosphorylated forms of beta-casein were selected for area and density measurements by means of the NIH-Image program. The larger area at approximately 26 kDa, isoelectric point 5.3, consisted of 1 to 3 closely linked spots, perhaps reflecting phenotype. The smaller spot 24kDa, isoelectric point 5.4, was always a single unit. Visual scanning of gels suggests a wide range of casein concentration. Computer comparison will allow a statistical analysis.