Serine protease inhibitor (PubMed:33666645). Strongly inhibits trypsin (Ki = 4 nM) and elastase (Ki = 4.8 nM) (PubMed:33666645). Also inhibits chymotrypsin with a Ki of 22 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.