Plasmin is an important degrading enzyme (EC 3.4.21.7) of many proteins of blood plasma but specifically of fibrin clots. This process is termed fibrinolysis.
It is a serine protease that is released as plasminogen into the circulation and activated by tissue plasminogen activator (tPA), thrombin, fibrin and factor XII (Hageman factor). It is inactived by alpha 2-antiplasmin, a serine protease inhibitor (serpin).
Apart from fibrinolysis, plasmin proteolyses proteins in various other systems: it activates collagenases , some mediators of the complement system and weakens the wall of the Graafian follicle (leading to ovulation). It cleaves fibrin, fibronectin, thrombospondin , laminin and von Willebrand factor.
Deficiency in plasmin may lead to thrombosis, as clots are not degraded adequately.
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