An alpha-amylase inhibitor from cranberry bean (Phaseolus vulgaris): its specificity in inhibition of mammalian pancreatic alpha-amylases and formation of a complex with the porcine enzyme.

A proteinaceous inhibitor that inhibits mammalian alpha-amylases was prepared from cranberry bean and examined for its reactivity with alpha-amylases from various origins. The cranberry bean alpha-amylase inhibitor (CBAI) exhibited inhibitory effects on pancreatic alpha-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 alpha-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 degrees 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 CABI were required to give 50% inhibition at pH 6.9 than at pH 5.5. Especially, both bovine and rat alpha-amylases were virtually unreactive to CBAI at pH 6.9.