Effect of temperature and some factors on gut α-amylase of the desert locust; Schistocerca gregaria Forsk. (Orthoptera:Acrididae)

Gut of 4th nymphal instar of the desert locust; Schistocerca gregaria Forsk. was analyzed to study the effect of ambient temperature and some factors controlling α-amylase activity (in vitro) as a key carbohydrase enzyme for carbohydrate digestion. The study might provide a basis for locust control in different environments conditions. Crude gut enzymes as α-amylase, cellulase, invertase and trehalase were extracted by gut homogenization and differential centrifugation up to 100,000×g. Invertase had the highest activity in the gut followed by amylase and trehalase, while cellulase had the lowest one. Increasing ambient temperature from 10 to 37 °C enhanced, in vivo, α-amylase activity which declined when environmental temperature increased more than 37 °C. In vitro experiments revealed that α-amylase. crude protein extract showed optimal activity at pH 6, 45 °C and 17.9 mg/ml soluble starch (substrate) concentration. Amylase was thermostable up to 50 °C, while it did not able to keep its major activity at 70 °C. The enzyme was more stable when exposed to acidic than to alkaline media.Vmax of α-amylase was 3.73 μmol glucose min−1mg protein−1. The results revealed that gut α-amylase had a relatively low affinity to soluble starch (high Km value), and low activation energy (0.451 kJ mol−1). Relatively high ambient temperature reduced α-amylase that might affect carbohydrates digestion and reduce locust nutrition.