Trypsin inhibitory activities of SdPI and its mutants.

The inhibitory activities of SdPI and its mutants on the hydrolysis of synthetic chromogenic substrates by trypsin were assayed in 100 mM Tris-HCl (pH 8.0), containing 10 mM CaCl2 at 25°C. Trypsin was pre-incubated with the inhibitor for 30 min. The reaction was initiated by addition of synthetic chromogenic substrates. Formation of p-nitroaniline was monitored continuously at 405 nm for 5 min. Inhibition constants of SdPI and mutants were determined by Lineweaver-Burk plots and further replotting of the slopes. Errors in Ki values are less than ± 10%.-, no inhibition detected.