An α-Amylase Inhibitor from Cranberry Bean (Phaseolus vulgaris): Its Specificity in Inhibition of Mammalian Pancreatic α-Amylases and Formation of a Complex with the Porcine Enzyme

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A proteinaceous inhibitor that inhibits mammalian α-amylases was prepared from cranberry bean and examined for its reactivity with α-amylases from various origins. The cranberry bean α-amylase inhibitor (CBAI) exhibited inhibitory effects on pancreatic α-amylases from the following mammals: pig, dog, cat, horse, sheep, cow, rabbit, guinea pig, rat, and mouse. CBAI showed a maximal inhibition at pH 5.5 against porcine pancreatic α-amylase (PPA). It was confirmed by gel filtration that a complex was formed in the 1:1 ratio between CBAI and PPA when they were incubated at 37°C for 30 min at pH 5.5. A similar inhibition pattern was also observed at pH 6.9 that is optimal for the amylase reaction, but much higher concentrations of CBAI were required to give 50% inhibition at pH 6:9 than at pH 5.5. Especially, both bovine and rat α-amylases were virtually unreactive to CBAI at pH 6.9.