Serine protease inhibitor (PubMed:33666645). Strongly inhibits trypsin (Ki = 7.1 nM) and almost completely inhibits elastase (PubMed:33666645). Also inhibits chymotrypsin (Ki = 19 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.