The individual or combined action of chymosin and plasmin on sodium caseinate or beta-casein in solution: effect of NaCl and pH

Although beta-casein appeared to be degraded by bovine plasmin slightly fas ter in a salt-free system than in a solution containing NaCl, increasing th e concentration of NaCl had little effect on the activity or specificity of the enzyme. The activity, but not the specificity, of bovine plasmin on be ta-casein was influenced by pH; the rate of hydrolysis proceeded in the ord er pH 8.4 > 6.5 > 5.4. Chymosin did not appear to degrade peptides produced from beta-casein by plasmin (i.e. gamma(1), gamma(2), gamma(3)-caseins and their corresponding proteose peptones). In sodium caseinate, alpha(s1)-cas ein was more susceptible to hydrolysis by chymosin than beta-casein. The ac tivity of chymosin on Na-caseinate increased with decreasing pH in the rang e of 6.5 to 5.4. Increasing concentrations of NaCl inhibited proteolysis to an extent that was dependent on the reaction pH. Bovine plasmin rapidly hy drolysed Na-caseinate to a wide range of peptides detectable by polyacrylam ide gel electrophoresis (PAGE) and it was also capable of degrading Na-case inate-derived peptides produced by chymosin to a similar range of peptides. (C) Inra/Elsevier, Paris.