HYDROLYSIS OF CAPRINE BETA-CASEIN BY PLASMIN

The proteolytic activity of plasmin on soluble caprine beta-casein (CN ) was studied in 50 mM Tris.HCl buffer, pH 8.0, at 37 degrees C. Elect rophoretic studies showed that hydrolysis of this protein results in a n electrophoretic pattern that is similar to the pattern obtained from plasmin hydrolysis of bovine PCN (gamma-CN and complementary N-termin al fragments), suggesting that plasmin probably attacks the same regio ns that are susceptible to cleavage in bovine beta-CN. As determined b y SDS-PAGE, the gamma-like components of caprine milk consisted of two fragments with relative molecular mass of 9200 and two with relative molecular mass of 21,400 that could differ in the level of phosphoryla tion. Apparently, the high molecular mass components are homologous to bovine beta-CN (f 29-209) (gamma(1)-CN), and the low molecular mass c omponents are homologous to bovine beta-CN (f 106-209) and beta-CN (f 108-209) (gamma(2)- and gamma(3)-CN). Complementary N-terminal fragmen ts had values for molecular masses in the range 13,600 to 8500 and ure a-PAGE patterns that were more complex than those obtained in bovine c asein because of the different phosphorylation levels in caprine beta- CN. These fragments were also present in the hydrolysate of whole capr ine casein that had been treated with plasmin.