PURIFICATION AND PARTIAL CHARACTERIZATION OF TWO ?-AMYLASE INHIBITORS FROM BLACK BEAN (Phaseolus vulgaris)

Two α-amylase inhibitors from black bean (Phaseolus vulgaris) were purified to homogencity using ammonium sulfate fractionation, DEAE-Sephadex chromatography, phenyl-Sepharose hydrophobic interaction chromatography and gel filtration with Sephadex G-100. 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 α-amylases and inactive against bacterial, mold, and plant α-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. I–2 is more resistant to heat denaturation than I-1.