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

Abstract

Although ~-casein appeared to be degraded by bovine plasmin slightly faster in a salt- free system than in a solution containing NaCI, increasing the concentration of NaCl had little effect on the activity or specificity of the enzyme. The activity, but not the specificity, of bovine plasmin on ~-casein was influenced by pH; the rate of hydrolysis proceeded in the order pH 8.4 > 6.5 > 5.4. Chymosin did not appear to degrade peptides produced from ~-casein by plasmin (i.e. y!' Y2' Y3-caseins and their corresponding proteose peptones). In sodium caseinate, as1-casein was more susceptible to hydrolysis by chymosin than ~-casein. The activityof chymosin on Na-caseinate increased with decreasing pH in the range 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 hydrolysed N a-caseinate to a wide range of peptides detectable by polyacrylamide gel electrophoresis (PAGE) and it was also capable of degrading Na-caseinate-derived peptides produced by chymosin to a sim- ilar range of peptides. © Inra/Elsevier, Paris. chymosin / plasmin / sodium caseinate / ~-casein / hydrolysis