ALPHA-AMYLASES FROM 3 SPECIES OF STORED GRAIN COLEOPTERA AND THEIR INHIBITION BY WHEAT AND CORN PROTEINACEOUS INHIBITORS

Two alpha-amylase isozymes were isolated from adults of both the rice weevil, Sitophilus oryzae, and the red flour beetle, Tribolium castaneum, and a single alpha-amylase from adults of the yellow mealworm, Tenebrio molitor. All of the purified enzymes had similar amino acid compositions as well as physical and chemical properties. The apparent molecular masses ranged from 53 to 58 kDa. Circular dichroism measurements revealed approx. 33% alpha-helical content. V(max) and K(m) values ranged from 1.33 to 5.98 mM min-1 mg-1 and 0.76 to 5.57 mg ml-1, respectively, using starch as the substrate. An alpha-amylase inhibitor from wheat (WRP-25) inhibited all five enzymes, whereas an inhibitor from corn inhibited only enzymes from the red flour beetle and yellow mealworm.