There are two inhibitors of plasmin in the plasma proteins of the human. α1-antiplasmin is heat-labile and migrates as an α1-globulin on electrophoresis. It combines non-dissociably with plasmin at a rate that depends on temperature.
α2-antiplasmin is relatively more heat-stable and migrates as an α2-globulin on electrophoresis. It combines dissociably with plasmin independently of temperature.