Serine protease inhibitor (PubMed:33666645). Inhibits trypsin (Ki=12nM) and weakly inhibits chymotrypsin with (Ki=460nm) (PubMed:33666645). Does not inhibit bacterial subtilisin (PubMed:33666645). Expressed in bulb (at protein level). Belongs to the Bowman-Birk serine protease inhibitor family.