Rates and Extents of Hydrolysis of Several Caseins by Pepsin, Rennin, Endothia parasitica Protease and Mucor pusillus Protease

The initial rates of hydrolysis, rates of hydrolysis and extents of hydrolysis after 1,440 rain reaction of whole, a-, fi-, and K-caseins by crystallized rennin, crystallized pepsin and purified M. pusillus protease and E. parasitica protease at pH 3.0, 3.5, 5.5 and 6.0 have been determined. The number of peptide bonds hydrolyzed was determined by the trinitrobenzene sulfonie acid method. E. parasitica protease generally had more activity than the other three enzymes on all substrates at all pHs. With whole, a-and K-caseins the initial rates and extents of hydrolysis decreased from pH 3.0 to 6.0 with a few exceptions. With all four enzymes the extent of hydrolysis of t-casein was lower at pH 3.0 than at pH 3.5. At pH 6.0, all four enzymes had the fastest initial rates of hydrolysis on K-casein followed in turn by o~-casein and t-casein. The initial rates of hydrolysis of t-casein at pH 6.0 were very low by all four enzymes. The extents of hydrolysis at pH 6.0 were in the order of a-, K-and t-casein except for E. parasitica protease where the order was a-, fl-and K-casein. With all four enzymes the extent of hydrolysis of fl-casein at pH 5.5 was much greater than at pH 6.0.