STUDIES ON PROTEOLYTIC DEGRADATION OF CAS EINS .1. EFFECT OF PLASMIN AND CHYMOSIN ON CASEIN IN A MODEL SYSTEM

The effect of plasmin and chymosin on alpha(s1)-, beta- and whole case in was investigated in simulated milk serum at pH 6.6 (for plasmin) an d pH 5.3 (for chymosin). At these optimal conditions both plasmin and chymosin hydrolysed the available caseins very intensively. Electropho retic analysis showed, that plasmin hydrolysed beta-casein completely after 6 h and alpha(s1)-casein only after 240 h. A complete degradatio n of the intact caseins by chymosin at pH 5.3 was reached already afte r 21 h. Peptides (rel. molecular mass <5000) were formed slowly by pla smin only after 72 h (hydrolysis of beta-casein) and after 144 h (hydr olysis of alpha(s1)-casein). Towards alpha(s1)-casein chymosin showed a particular specificity producing 7 peptides (rel. molecular mass <50 00) after 21 h of incubation. Additional studies showed that the elect rophoretically detectable plasmin degradation products of alpha(s1)-ca sein were rapidly hydrolysed by chymosin after the change of pH-value.