CHARACTERIZATION AND FUNCTIONAL-PROPERTIES OF THE ALPHA-AMYLASE INHIBITOR (ALPHA-AI) FROM KIDNEY BEAN (PHASEOLUS-VULGARIS) SEEDS

Alpha-amylase inhibitor (alpha-AI) from kidney bean (Phaseolus vulgari s L. cv Tendergreen) seeds has been purified to homogeneity by heat tr eatment in acidic medium, ammonium sulphate fractionation: chromatofoc using and gel filtration. Two isoforms, alpha-AI1 and alpha-AI1', of 4 3 kDa have been isolated which differ from each other by their isoelec tric points and neutral sugar contents. The major isoform alpha-AI1 in hibited human and porcine pancreatic alpha-amylases (PPA) but was devo id of activity on alpha-amylases of bacterial or fungal origins. As sh own on the Lineweaver-Burk plots, the nature of the inhibition is expl ained by a mixed non-competitive inhibition mechanism. alpha-AI1 forme d a 1:2 stoichiometric complex with PPA which showed an optimum pH of 4.5 at 30 degrees C. Owing to the low optimum pH found for alpha-AI ac tivity, inhibitor-containing diets such as beans or transgenic plants expressing (alpha-AI should be devoid of any harmful effect on human h ealth. (C) 1997 Elsevier Science B.V.