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Purification and Characterization of a New Class of Insect α-Amylase Inhibitors from Barley

¹Department of Agronomy, University of Wisconsin-Madison, 501 N. Walnut St., Madison, WI 53705. ²USDA, Agricultural Research Service, Cereal Crops Research Unit, 501 N. Walnut St., Madison, Wisconsin 53705. Corresponding author. E-mail: bljones@facstaff.wisc.edu Mention of a product is for informational purposes only and is not meant to imply recommendation by the U. S. Department of Agriculture over others that may be suitable. ³USDA-ARS Western Regional Research Center, 800 Buchanan St., Albany CA 94710. Present address: Inhale Therapeutic Systems, 1001 East Meadow Circle, Palo Alto CA 94303.

Barley seeds contain proteins that apparently protect them against attack by microorganisms and insects. Studies of these barley defensive proteins may lead to the development of barleys with improved natural resistance to pests. We have purified two low molecular weight proteins, designated BIα1 and BIα2, from barley grain, using ion-exchange chromatography and reversed-phase and gel-permeation high-performance liquid chromatography (HPLC). Both BIα1 and BIα2 inhibited insect (yellow meal worm, Tenebrio molitor) α-amylase activities. For the T. molitor α-amylase, the IC50 values of BIα1 and BIα2 were 80 μg/mL (12.5 μM) and 34 μg/mL (6.8 μM), respectively. Neither protein inhibited either human salivary α-amylase, barley α-amylase, or trypsin activities. N-terminal amino acid sequences of the inhibitors were highly homologous with those of the plant proteins called defensins. The first 20 N-terminal amino acids of BIα2 were identical to those of γ-hordothionin, but neither BIα1 nor BIα2 protein showed any homology with the chloroform-methanol (CM) soluble protein amino acid consensus sequence. The two inhibitors therefore apparently comprise another group of low molecular weight barley proteins that inhibit the α-amylase activities of some insects that attack cereal grains.