Kinetics of the interaction of pancreatic alpha-amylase with a kidney bean (Phaseolus vulgaris) - amylase inhibitor

ABSTRACT An amylase inhibitor isolated from black beans (Phaseolus vulgaris) can completely inhibit porcine pancreatic α‐amylase forming a 1:1 stoichiometric complex. The kinetic pattern of complex formation is pH dependent. At pH 5.5 it follows a first order reaction with rate constant of 0.029 min−1 and 0.017 min−1 at 37°C and equimolar inhibitor and enzyme concentration, respectively, of 10−8 M and 10−9 M. At pH 6.9 it is a second order reaction, with a rate constant of 0.25 × 106 M−1 min−1 at 37°C, with 4 × 10−8 M concentrations of enzyme and inhibitor. The dissociation constants of the enzymeinhibitor complex are 1.7 × 10−10 M at pH 5.5 and 4.4 × 10−9 M at pH 6.9, at 37°C. The kinetic data obtained at pH 5.5 suggested the formation of an initial reversible complex followed by a conformational change step. The complex can be dissociated either in acid pH (4.3) or at pH values higher than 6, 5 with partial recovery of the amylase activity.