Pectinase and cellulase activity in the digestive system of the elm leaf beetle, Xanthogaleruca luteola Muller (Coleoptera: Chrysomelidae)

Abstract

The elm leaf beetle, Xanthogaleruca luteola, is a serious pest of elm trees in urban areas. Partial biochemical characterization of pectinases and cellulases was conducted using the larval digestive system of the pest. Midgut extracts from larvae showed optimum activity for pectinase and cellulase against pectin and carboxymethyl cellulose, respectively, under acidic conditions (pH 6). Pectinases and cellulases were respectively more stable under acidic conditions (pH 4–7) and slightly acidic conditions (pH 5–7) than under highly acidic and alkaline conditions. However, the enzymes were more stable in slightly acidic conditions (pH 6) when incubation time was increased. Maximum activity for the pectinases and cellulases incubated at different temperatures was observed at 45 and 50°C, respectively. Mg2+ remarkably increased pectinase activity, and cellulase activity increased significantly in the presence of Ca2+ and Mg2+. Sodium dodecyl sulfate significantly decreased pectinase and cellulase activity. The Michaelis–Menten constant (KM) and the maximal reaction velocity (Vmax) values for pectinase were 2mg·mL−1 and 0.017mmol·min−1·mg−1 protein toward pectin, respectively. Zymogram analyses revealed the presence of one and five bands of pectinase and cellulase activity, respectively, in the larval midgut extract.