Biochemical characterization of digestive carbohydrases from Xanthogaleruca luteola and inhibition of its α-amylase by inhibitors extracted from the common bean

Xanthogaleruca luteola M?ll. (Col.: Chrysomelidae) is a major urban insect pest on elm trees in Iran. Digestion in the alimentary canal of the elm leaf beetle is facilitated by some carbohydrases which are responsible for the digestion of carbohydrates. The presence of digestive carbohydrases was determined in the digestive system of adult and last larval instar of the elm leaf beetle. The specific activity of ?-amylase in the digestive system of adult females and last larval instars were 0.49? 0.05 and 0.72? 0.07 ?mol/min/mg protein, respectively. Also, the amylase activity in the midgut of the last larval instar was 3.125- and 4.16-fold higher than that its activity in the foregut and hindgut, respectively. Results showed that optimum activity for ?-amylase was found at pH 5. As calculated from Lineweaver-Burk plots, the Km values for ?-amylase were 0.64 and 1.44 mg/ml, when glycogen and starch were used as substrates, respectively. The effect of pH and temperature on ?- and ?-glucosidase and ?- and ?-galactosidase activities was determined in the digestive system of X. luteola. Results showed that the activity of ?- and ?-glucosidases in adult females was higher than in larvae, but the ?galactosidase activity in larvae was more than that of the adult. In adult females the glucosidase activity was higher than the galactosidase activity. The zymogram pattern in the native gel revealed that X. luteola ?-amylase, ?-glucosidase and ?-galactosidase in the digestive system had one, three and one isoforms. ?-amylase inhibitors, purified from Phaseolus vulgaris L. with an ion-exchange DEAE cellulose column showed good inhibitory activity on X. luteola gut ?-amylase.