Requirement of human plasmin for streptokinase activation of bovine plasminogen

Abstract

Abstract It was recently reported that while native streptokinase (SK) cannot activate bovine plasminogen (plgn), a derivative of SK (SK 1 ) prepared by interaction of SK with human plasminogen was capable of activating bovine plasminogen. Evidence is now presented to show that the activator activity of SK 1 towards bovine plasminogen requires the presence of trace amounts of human plasmin. With an assay for plgn or plasmin which permits detection of 0.01 CTA units, we found small amounts of plasmin in our SK 1 preparations. When SK 1 preparations were completely freed of plasmin by passage through a lysine-sepharose column, bovine activator activity disappeared but human activator activity remained. Addition of human plasmin (ogen) to the column-treated SK 1 preparations restored bovine activator activity. When the plasmin inhibitors, p-nitrophenyl-p-guanidinobenzoate or pancreatic trypsin inhibitor, were added to SK 1 preparations, or when plasmin was inactivated by reduction and alkylation, bovine activator activity was lost but human activator activity remained.