Serine protease inhibitor (PubMed:33666645). Strongly inhibits trypsin (Ki = 0.22 nM) and very weakly inhibits chymotrypsin (Ki = 1200 nM) (PubMed:33666645). Does not inhibit bacterial subtilisin (PubMed:33666645). Expressed in bulb (at protein level). Belongs to the Bowman-Birk serine protease inhibitor family.