Biochemical characterization of midgut, salivary glands and haemolymph α-amylases of Naranga aenescens

Naranga aenescens L. (Lepidoptera Noctuidae), commonly known as the rice green caterpillar, is one of the most damaging pests of the rice crop in Iran causing extensive defoliation. Study of digestive enzymes is so imperative to reach and apply new pest management technologies. Amylases have an important role in the final stages of carbohydrate digestion. α-amylases activities were determined in midgut, haemolymph and salivary glands homogenates of N. aenescens larvae. The activities of α-amylases in the midgut, salivary glands and haemolymph of 5 th instar larvae were 2.4 ± 0.04, 2 ± 0.06 and 1.2 ± 0.06 µmol/min/mg proteins, respectively. Zymogram pattern in the native gel revealed that N. aenescens α-amylases in midgut, salivary glands and haemolymph had two isoform. Results showed that the optimal pH for α-amylases in midgut, salivary glands and haemolymph were 8, 9 and 9, respectively. Also optimal temperature for α-amylases activity in midgut was 60 °C and salivary glands and haemolymph were 50 °C. As calculated from Lineweaver-Burk plots, the Km for midgut, salivary glands and haemolymph were about 0.07, 0.14 and 0.14 mg/ml and the Vmax were 0.2, 0.08 and 1.32 µmol/min. Hg + , Hg 2+ and Mn 2+ decreased enzyme activity even completely in all three tissue of N. aenescens α-amylases, whereas the addition of Na + , K + , Co 2+ , Mg 2+ , Ca 2+ and Fe 2+ increased their activity. α-amylase activity in N. aenescens is essential for developing a method for insect control, such as the use of an α-amylase inhibitor as a biocontrol agent and over expression of α-amylase inhibitor in transgenic plant.