Interaction of wheat monomeric and dimeric protein inhibitors with α-amylase from yellow mealworm (Tenebrio molitor L. larva)

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Abstract
The highly purified .alpha.-amylase from T. molitor L. larva (yellow mealworm) reversibly combines with 2 closely related homogeneous glycoprotein inhibitors, 1 dimeric (termed inhibitor 0.19) and 1 monomeric (termed inhibitor 0.28), from wheat flour. Using spectroscopy and kinetic studies, molar combining ratios for the amylase-inhibitor-0.19 and amylase-inhibitor-0.28 complexes were 1:1 and 1:2, respectively. Two amylase-inhibitor-0.19 complexes with different retention volumes on Bio-Gel P-300 and only 1 amylase-inhibitor-0.28 complex were observed. Dissociation constants of the amylase-inhibitor-0.19 and amylase-inhibitor-0.28 complexes were 0.85 nM and 0.13 mM, respectively. A strong tendency of both complexes to precipitate under an ultracentrifugal field was observed; the minimum MW calculated for the 2 complexes under such conditions was .apprx. 95,000. The 2 complexes showed different spectra indicating involvement of structurally related or identical tryptophyl side chains in the binding of inhibitors 0.28 and 0.19 to the amylase. A model summarizing the main features of the inhibition of the insect amylase by the 2 wheat protein inhibitors is proposed.