Mechanism of fibrin-specific fibrinolysis by staphylokinase: Participation of α2-plasmin inhibitor

Abstract

When the extent of plasminogen activation by staphylokinase (SAK) or streptokinase (SK) was measured in human plasma, SAK barely induced plasminogen activation, whereas SK activated plasminogen significantly. When the plasma was clotted with thrombin, the plasminogen activation by SAK was markedly enhanced, but that of SK was little enhanced. Similarly, in a purified system composed of plasminogen, fibrinogen and α 2-plasmin inhibitor ( α 2-PI, α 2-antiplasmin), such a fibrin clot increased the activity of SAK significantly. However, when α 2-PI was removed from the reaction system, enhancement of the SAK reaction was not observed. In addition, SAK as distinct from SK, showed very little interference with the action of α 2-PI. Plasminogen activation by SAK is thus essentially inhibited by α 2-PI, but this reaction is not inhibited in fibrin clots. These results suggest that SAK forms a complex with plasminogen, Which binds to fibrin and induces fibrinolysis.