plasmin (fibrinase; fibrinolysin) An enzyme, present in blood plasma, that breaks down a blood clot by destroying the fibrin threads of the clot and by inactivating factors involved in blood clotting, such as prothrombin and the clotting factors. This occurs during fibrinolysis. Plasmin is derived from an inactive precursor, plasminogen.

plasmin (fibrinolysin) (plaz-min) n. an enzyme that digests the protein fibrin. Its function is the dissolution of blood clots (see fibrinolysis).