Purification of fat body glutathione S‐transferase from the desert locust Schistocerca gregaria: investigation of flavonoid inhibitory effects on enzyme activity

Focus on the development of botanical insecticides such as polyphenols may represent an alternative method to chemical control. In the present study, total glutathione concentration and its related antioxidant enzymes in foregut, midgut, hindgut and fat body homogenates of the desert locust Schistocerca gregaria are examined. Glutathione S‐transferase (GST) activity exhibits a significantly higher value in fat bodies compared with other tissues. A simple and reproducible procedure for the purification of S. gregaria fat body GST is established and the purified enzyme is shown to be homogenous. The purified GST displays a typical Michaelis behaviour with respect to its substrates. Characterization of the GST, including optimum pH, substrate specificity and inhibitor effects, is carried out. The ability of some flavonoids to inhibit S. gregaria fat body GST activity is examined. High‐performance liquid chromatography analysis indicates that the major components in Glycyrrhiza glabra roots are 18α‐glycyrrhetinic acid, quercetin and rutin, and the major components in Hibiscus sabdariffa calyx are cyanidin 3‐O‐glucoside chloride and delphinidin. Quercetin and delphinidin chloride exhibit strong GST inhibition and the inhibition type is determined for both. Rutin shows a smaller inhibitory effect, whereas 18α‐glycyrrhetinic acid and cyanidin have no effect. Inhibition of S. gregaria fat body GST activity would be expected to prevent, or at least delay, the development of resistance to chemical pesticides. Among the examined levels of the antioxidant enzymes, total glutathione concentration and its related enzymes in foregut, midgut, hindgut and fat body crude homogenates of S. gregaria GST activity exhibit a significantly higher value in fat bodies compared with other tissues. Some flavonoids that are detected in H. sabdariffa calyx and G. glabra root extracts are the most effective inhibitors of the purified S. gregaria fat body GST activity. Inhibition of S. gregaria fat body GST activity by quercetin and delphinidin (major compounds detected by HPLC) would be expected to prevent, or at least delay, the development of resistance to chemical pesticides.