Effects of alpha 2-plasmin inhibitor on plasminogen activation by staphylokinase/plasminogen complex

Using a stable cross-linked SAK/plg complex, the effects of alpha 2-plasmin inhibitor on plasminogen activation by SAK were investigated. alpha 2-Plasmin inhibitor inhibited dose-dependently plasminogen activation by the SAK/plg complex. When FCB-2 or EACA was added to the reaction mixture of SAK/plg complex and alpha 2-plasmin inhibitor, the inhibitory activity of alpha 2-plasmin inhibitor was abolished and the enzymatic activity of the complexes was restored. alpha 2-Plasmin inhibitor inhibited the activity of the SK/plg complex, but neither FCB-2 nor EACA restored the plasminogen activator activity in the mixture of SK/plg complex and alpha 2-plasmin inhibitor. Using 125I-labeled SAK/plg complex or SK/plg complex, the reaction of the complex with alpha 2-plasmin inhibitor was analyzed. The SAK/plg complex produced a new complex with alpha 2-plasmin inhibitor. The formation of a new high molecular weight complex with alpha 2-plasmin inhibitor was abolished by both EACA or FCB-2. With regard to the SK/plg complex, neither EACA nor FCB-2 suppressed the complex formation with alpha 2-plasmin inhibitor. These findings indicate that the SAK/plg complex binds to fibrin, and that this complex expresses plasminogen activator activity without being affected by alpha 2-plasmin inhibitor.