Activity of Bacillus polymyxa protease on components of the plasmin system in milk

The activity of a metalloprotease produced by Bacillus polymyxa toward the plasmin system was studied in both buffer and milk. Chromogenic assays were carried out to monitor effects of the protease on plasmin activity in a buffer system. Among the plasmin system components, plasminogen was most affected by the protease. Hydrolysis of plasminogen was identified and visualized using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and casein-SDS-PAGE, respectively. Results confirmed that B. polymyxa protease cleaved bovine plasminogen, generating a plasmin-like activity. Kinetic parameters of the protease showed that its activity on plasminogen can be physiologically relevant where significant impact on plasminogen activation in milk can occur. This finding was further confirmed when, during refrigerated storage, a significant increase (P<0.01) in plasmin-like activity was observed in protease-treated pasteurized milk. Results of this study confirmed the interaction of the B. polymyxa protease with the plasmin system by acting as a plasminogen activator.