Potent inhibitor of serine proteases plasma kallikrein, plasmin and coagulation factor XIIa. Weak inhibitor of serine proteases trypsin and coagulation factor Xa. Does not inhibit the serine proteases chymotrypsin, elastase or thrombin. Inhibits kinin release from HMW-kininogen by kallikrein in vitro. Belongs to the protease inhibitor I3 (leguminous Kunitz-type inhibitor) family.