A proteolytic enzyme that can digest many proteins through the process of hydrolysis. Plasmin is found in plasma in the form of plasminogen, which is an inert precursor or zymogen; one site of synthesis is the liver. Plasma also contains inhibitors that limit either the transformation of plasminogen to plasmin (plasminogen activator inhibitors) or the action of plasmin (principally α₂-antiplasmin and α₂-macro-globulin).