Mode of action of the Kunitz trypsin and the Bowman-Birk proteinase inhibitors from soya bean against trypsins and chymotrypsins

The Kunitz soya bean trypsin inhibitor maximally binds about 1.4 mol/mol bo vine and human trypsin and also small amounts (about 0.1 mol/mol) of bovine and human chymotrypsin. The two trypsins are bound at arginine(63) and a f urther arginine, and the two chymotrypsins at tyrosine(62). The Bowman-Birk soya bean proteinase inhibitor maximally binds about 2 mol/mol of any of t he four enzymes. The two trypsins are bound at lysine(16) and a further lys ine, and the two chymotrypsins at leucine(43) and a further leucine or phen ylalanine.