Alpha-amylase inhibitor Ž. Ž . a-AI from kidney bean Phaseolus Õulgaris L. cv Tendergreen seeds has been purified to
homogeneity by heat treatment in acidic medium, ammonium sulphate fractionation, chromatofocusing and gel filtration.
Two isoforms, a-AI1 and a-AI1X
, of 43 kDa have been isolated which differ from each other by their isoelectric points and
neutral sugar contents. The major isoform a-AI1 inhibited human and porcine pancreatic a-amylases PPA but was devoid Ž .
of activity on a-amylases of bacterial or fungal origins. As shown on the Lineweaver–Burk plots, the nature of the
inhibition is explained by a mixed non-competitive inhibition mechanism. a-AI1 formed a 1:2 stoichiometric complex with
PPA which showed an optimum pH of 4.5 at 308C. Owing to the low optimum pH found for a-AI activity,
inhibitor-containing diets such as beans or transgenic plants expressing a-AI should be devoid of any harmful effect on
human health. q 1997 Elsevier Science B.V.