Purification and Characterization of Midgut α-Amylase in a Predatory Bug, Andralus spinidens

α-Amylases are widespread enzymes that catalyze endohydrolysis of long α-1,4-glucan chains such as starch and glycogen. The highest amylolytic activity was found in 5th instar nymphs and midgut of the predatory bug, Andrallus spinidens F. (Hemiptera: Pentatomidae). The α-amylase was purified following a three-step procedure. The purified α-amylase had a specific activity of 13.46 U/mg protein, recovery of 4.21, purification fold of 13.87, and molecular weight of 21.3 kDa. The enzyme had optimal pH and temperature of 7 and 45°C, respectively. Na+, Mn+, Mg2+, and Zn2+ significantly decreased activity of the purified α-amylase, but some concentrations of K+, Ca2+, and Cu2+ had the opposite effect. EDTA, EGTA, and DTC significantly decreased enzymatic activity, showing the presence of metal ions in the catalytic site of the enzyme. Kinetic parameters of the purified α-amylase showed a Km of 3.71% in starch and 4.96% for glycogen, suggesting that the enzyme had a higher affinity for starch.