Serine protease inhibitor (PubMed:33666645). Inhibits trypsin (Ki = 41 nM) and weakly inhibits chymotrypsin (Ki = 410 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.