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

Abstract

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 Xg. 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 17.9mg/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.V max of α-amylase was 3.73 μmol glucose min −1 mg protein −1 . The results revealed that gut α-amylase had a relatively low affinity to soluble starch (high K m 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.