Functionally this inhibitor is unusual in that it stoichiometrically inhibits trypsin in a molar ratio of 1:2. The specificities and functions of this superfamily of inhibitors depend not only on the active sites within the domains, but also upon the amino acid composition, and resulting molecular conformation, surrounding these regions. Three isoinhibitors are also found whose amino ends differ slightly from that shown. Belongs to the Bowman-Birk serine protease inhibitor family.