Serine protease inhibitor (PubMed:33666645). Weakly inhibits trypsin (Ki = 167 nM) (PubMed:33666645). Does not inhibit bacterial subtilisin or mamallian chymotrypsin (PubMed:33666645). Expressed in bulb (at protein level). Belongs to the Bowman-Birk serine protease inhibitor family.