Figure 2.

Scheme of the plasminogen–plasmin system. Inactive plasminogen is converted into plasmin as a result of an action of plasminogen activators (natural: urokinase plasminogen activator or tissue plasminogen activator, or synthetic: streptokinase). Plasmin then enables the degradation of fibrinogen (a plasma protein) as well as the degradation of the fibrin clot into fibrin cleavage products. The unbound circulating fibrinogen is converted into fibrin clot by thrombin. The formation of plasmin from plasminogen can be inhibited by antifibrinolytic drugs (Ahx). The interaction of Ahx with plasminogen or plasmin, as well as plasmin with fibrin or fibrinogen, is mediated by lysine binding sites, not enzymatic active sites of plasmin. Green arrows = activation, red arrows = inhibition.