Full Length Research Paper

Biochemical characterization of digestive amylase of wheat bug, Eurygaster maura (Hemiptera: Scutelleridae)

Sultan Ravan¹, Mohammad Mehrabadi² and Ali R. Bandani^2*

¹Plant Protection Department, Faculty of Agriculture, University of Zabol, Zabol, Iran.

²Insect Physiology and Molecular Biology Lab. Insect Physiology and Molecular biology Laboratory Plant Protection Department, School of Plant Protection and Horticultural Sciences, University of Tehran, Karaj, Iran.

*Corresponding author. E-mail: abandani@ut.ac.ir. Tel: +98- 261- 2818705.

Fax: +98-261- 2238529.

Accepted 27 March, 2009

   Abstract

Biochemical characterization of α-amylase in the midgut and salivary glands of Eurygaster maura was conducted. Results showed that α-amylase activities were present in the salivary glands and gut. The activity of α-amylase in the midgut and in the salivary glands was 0.098 and 0.057 U/ml, respectively. The pH of salivary glands and the gut was determined to be in the range of 5- 5.5 (for the salivary glands) and in the range of 6-6.5 (for the gut), using staining indicator. The optimum pH and temperature for salivary glands and midgut amylase activity was 6-7 and 35-40ºC, respectively. The stability of amylase was highest in the acidic pH (4-5). Ethylenediamine tetraacetic acid (EDTA), urea, sodium dodecyl sulfate (SDS) and Mg²⁺ inhibited the enzyme activity but, NaCl and KCl enhanced enzyme activity. Based on linear regression analysis of reciprocal starch concentration versus reciprocal amylase activity K_m and V_max were 0.11% and 0.04 mM maltose/min for midgut amylase and 0.298% and 0.071 mM maltose/min for salivary amylase, respectively. Sodium dodecyl sulfate electrophoresis (SDS-PAGE) showed that both midgut and salivary glands contain isozymes.

Key words: Eurygaster maura, digestive amylase, biochemical characterization, kinetic study.