Purification and partial characterization of two alpha-amylase inhibitors from black bean (Phaseolus vulgaris)

Two alpha -amylase inhibitors from black bean (Phaseolus vulgaris ) were purified to homogeneity. The inhibitors were designated I-1 and I-2 based on their order of elution from the phenyl-Sepharose column. Both inhibitors are mannose containing glycoproteins, composed of subunits; active against porcine pancreatic, human salivary, and insect alpha -amylases and inactive against bacterial, mold and plant alpha -amylases. The inhibitors I-1 and I-2 have molecular weights of 49,000 and 47,000 and isoelectric points 4.93 and 4.86, respectively. Both inhibitors have similar amino acid compositions and are rich in aspartic acid, serine, glutamic acid, valine, and threonine and are low in sulfur containing amino acids.