Biochemical characterization of α- and β-glucosidases in alimentary canal, salivary glands and haemolymph of the rice green caterpillar, Naranga aenescens M. (Lepidoptera: Noctuidae)

Abstract

The biochemical properties of α- and β-glucosidase in salivary glands, alimentary canal and haemolymph of Naranga aenescens larvae, one of the most damaging pests of the rice crop in Iran, were investigated. The specific activity of α-glucosidases were 3.88, 2.74 and 1.58 μmol/min per mg protein in the alimentary canal, salivary glands and haemolymph of last instar larvae, respectively. The specific activity of β-glucosidases were 1.27, 0.077 and 0.414 μmol/min per mg protein in the alimentary canal, salivary glands and haemolymph of last instar larvae, respectively. The optimal pH for α-glucosidases were 6.0, 6.0–8.0 and 6.0 and the maximum activity for β-glucosidases were obtained at pH 6.0, 5.0–7.0 and 5.0 in alimentary canal, salivary glands and haemolymph, respectively. The optimum temperatures for β-glucosidases were determined at 55°C in alimentary canal, 35–45°C in salivary glands and 55°C in haemolymph, whereas the α-glucosidases reached their optimum at 45°C in all three tissues. Effect of metal ions on the activity of α- and β-glucosidases showed that K+ (20 mM) and Mg2+ (10 and 20 mM) increased N. aenescens α- and β-glucosidases activities from salivary glands, while Ca2+ increased α- and β-glucosidases activities in haemolymph. In the presence of Fe2+, Mn2+, Hg+ and Zn2+ (10, 20 mM) and Hg2+ (20 mM), these enzymes from all tissues were completely inactivated. K m values were estimated for the α-glucosidases as 3.96, 0.547 and 3.084 mM and for β-glucosidases as 1.93, 1.014 and 1.93 mM in the alimentary canal, salivary gland and haemolymph, respectively. The zymogram analyses of N. aenescens crude extracts indicated the presence of at least two isoforms for α-glucosidase and one isoform for β-glucosidase.