Human Casein. III. DEAE-Celluslose-Urea Chromatography of Human Casein and Dephosphorylation of Casein Fractions

Human casein was separated into at least 11 fractions by DEAE cellulose column chromatography in 3.3 M urea.Addition of 2-mercaptoethanol did not inlprove sharpness of peaks, nor homogeneity of fractions.Electrophoretie mobility of the main six fractions increased with phosphorus content.Human fl-casein A through E was readily dephosphorylated by phosphoprotein phosphatase from beef spleen.Partial dephosphorylation of human fi-casein A and bovine fi-casein was accompanied by the appearence of five new components with lower mobilities and gel eleetrophoretie patterns of these components resembled those of human casein's main six components.Dephosphorylated human fl-casein A through E had the slowest-moving band corresponding to phosphorus-free fl-easein F on gel electrophoresis.Human fl-casein A, the most highly phosphorylated fraction resembled bovine fi-casein in phosphorus content, calcium sensitivity, and electrophoretic mobility.Human fi-caseins, main six components of human casein, are composed of a single protein with 0 to 5 atoms of phosphorus per molecule.