Susceptibility of .KAPPA.-casein components to various proteases.

Abstract
In order to clarify the function of the carbohydrate moiety of bovine .kappa.-casein, .kappa.-casein components having different carbohydrate contents were prepared by DEAE-cellulose chromatography. Five adsorbed fractions so obtained had an identical peptide chain and contained carbohydrate moieties of increasing size in the order of components P-2, P-3, P-4, P-5 and P-6. The susceptibility of .kappa.-casein components, having different carbohydrate contents, to various proteases was examined. .kappa.-Casein components were subjected to calf rennin [chymosin; EC 3.4.23.4], bovine trypsin [EC 3.4.21.4], .alpha.-chymotrypsin [EC 3.4.21.1], pronase [EC 3.4.24.4] and human plasmin [EC 3.4.21.7]. The component containing a larger carbohydrate moiety was less susceptible to hydrolysis than the component containing a smaller carbohydrate moiety. Rennin, trypsin, .alpha.-chymotrypsin and pronase hydrolyzed each component with a different reaction rate. Human plasmin hydrolyzed component P-2, but did not hydrolyze component P-5. These results indicate that the carbohydrate moiety of .kappa.-casein affected the susceptibility of .kappa.-casein components to various proteases.

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