Competitively inhibits trypsin stoichiometrically at the molar ratio of 1:1. Also inhibits chymotrypsin. Activity unaffected from pH 1-10. Loses 34% of its activity after 2 hours at pH >12 and 65% of its activity after 4 hours at pH >12. Retains over 90% of its activity after incubation at between 25 and 55 degrees Celsius for 1 hour. Heterodimer of an alpha and a beta chain linked by a disulfide bond. Belongs to the protease inhibitor I3 (leguminous Kunitz-type inhibitor) family.