Inhibits trypsin, plasmin, human plasma kallikrein, chymotrypsin and factor XIIa activity. Heterodimer of an alpha and a beta chain linked by a disulfide bond. Abundant in dry seeds. There are two isoforms of the beta chain with slightly different molecular masses: 4764 and 4765 Da. These isoforms differ in their N- and C-terminal amino acids. Belongs to the protease inhibitor I3 (leguminous Kunitz-type inhibitor) family.