Suitability of animals' purified milk caseins and their subunit kappa-caseins as substrates for subtilisin and trypsin

Acid casein and K-casein were purified from different species of animal's m ilk, such as cow, sheep, goat, and water buffalo. These caseins were used a s substrates for commercially available subtilisin and trypsin. It was established that, when acid caseins were used as a substrate for sub tilisin, cow acid casein was found to be a better substrate for the enzymes , compared to other animals' milk casein. It was suggested that this acid c asein has significantly more aromatic amino acids, as compared to arginine and lysine. K-m and V-max values, which were obtained for cow K-casein, showed that cow K-casein was a better susbstrate for trypsin than the others, suggesting t hat cow Ic-casein has a rich content of lysine, arginine, and aromatic amin o acids by comparison with the others. The calculated C/N ratio also suppor ts this suggestion.