Inhibitors of trypsin and chymotrypsin. HGGI-III has a higher activity than HGGI-I or HGGI-II. HGI-III exists in a state of equilibrium between monomer, homodimer and trimer, with homodimer being the predominant form. The homodimer is stabilized by the non-covalent interaction between Lys-24 of one subunit and Asp-76 of the other subunit. The homodimer is more thermostable than the monomer. HGGI-I, HGGI-II and HGGI-III exist as monomers. HGI-III is expressed before germination. HGGI-I, HGGI-II and HGGI-III are expressed after germination. HGGI-I, HGGI-II and HGGI-III are produced by proteolysis of the N- and C-termini of HGI-III. Belongs to the Bowman-Birk serine protease inhibitor family.