On the activity and specificity of cardosin B, a plant proteinase, on ovine caseins

The proteolytic activity of cardosin B, an aspartic proteinase from the thistle, Cynara cardunculus, on ovine αs-caseins and β-caseins (independently or present together in sodium caseinate) was followed by urea polyacrylamide gel electrophoresis and reversed phase high performance liquid chromatography. This enzyme degraded both types of caseins, but not to the same degree. In sodium-caseinate, by 10 h at 30°C, αs-caseins were more susceptible to proteolysis by cardosin B than β-casein whereas, in isolated form, the reverse was observed. Sequencing of the peptides produced by hydrolysis of Na-caseinate showed that the major cleavage sites in αs1-casein were Leu156-Asp157 and Trp164-Tyr165 whereas, in β-casein, they were Leu127-Thr128, Leu165-Ser166 and Leu90-Tyr191. The bonds Trpl64-Tyr165 and Leu165-Ser166 were the most susceptible to cardosin B when this enzyme acted upon isolated αs1- and β-casein, respectively.