Identification and characterization of hydrolytic enzymes from the midgut of the cotton bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

Midgut hydrolytic enzymes of Helicoverpa armigera Hubner (Lepidoptera: Noctuidae) were identified and partially characterized. Km, Vmax, optimum pH, and specific activity were determined for proteolytic enzymes and alpha-amylases. All hydrolytic enzyme activity had an optimum pH value in the alkaline pH range. We observed major serine protease activity, together with minor cysteine-like activity, the former being significantly inhibited by soybean trypsin inhibitor (SBTI) and aprotinin. Moreover, different degrees of inhibition were observed with synthetic protease inhibitors. Electrophoretic methods revealed 3 isozymes of alpha-amylases, of which 2 had higher molecular weight and were more active than the other. Inhibition of amylolytic activity was observed with wheat alpha-amylase inhibitor (WAAI), whereas partially purified maize, chickpea, and bean seed crude extracts did not exhibit inhibitory activity toward alpha-amylases. To the best of our knowledge this is the first report on the properties of alpha-amylases from Helicoverpa armigera and the effects of several plant-originated a-amylase inhibitors on them.