A kinetic analysis of the inhibition of rat and bovine trypsins by naturally occurring protease inhibitors

The dissociation constants (Ki) of the interaction of 10 naturally occurring inhibitors with rat anionic and bovine trypsins were determined employing three independent methods. Both enzymes bound very tightly (Ki less than 10(-9)) to bovine pancreatic, lima bean, and the Kunitz soybean inhibitors. With the exception of ovomucoid, rat trypsin bound more tightly than bovine trypsin to inhibitors derived from navy bean, lima bean, soybean (Bowman-Birk) and potato and to ovoinhibitor, leupeptin and antipain. These findings emphasize the caution that must be exercised in the interpretation of experiments involving the inhibition of trypsins from heterologous species of animals by naturally occurring inhibitors.