Glutathione Stransferases (GSTs) have been purified from more than 24 insect species, including Lepidoptera, Diptera, Coleoptera, Dictyoptera, and Hymenoptera. These transferases exist in multiple forms; as many as eight isozymes were found in midguts and fat bodies of fall armyworm larvae. Molecular weights of insect GSTs are within the range of 35 000-63 000. They consist of two subunits (homodimers and heterodimers) of molecular weight between 19000 and 35000. Insect GSTs metabolize various electrophilic xenobiotics, including halogenated compounds, nitro compounds, α,β-unsaturated compounds, isothiocyanates, organothiocyanates, organophosphates, and oxides. At least 55 chemicals have served as substrates for GSTs in insects. GSTs have been induced by numerous xenoblotlcs, including insecticides, drugs, host plants, and allelochemicals in over 21 species of insects. Among these inducers, insecticides (organochlorines), host plants (umbellifers and crucifers), and allelochemicals (furanocoumarins, indoles, and flavonoids) are the most potent inducers of the enzymes. Species differences in enzyme inducibility were observed in Lepidoptera. GST induction in insects was associated with increased GST mRNA levels indicating de novo synthesis of the enzyme. GSTs have been implicated in the resistance to insecticides and allelochemicals in insects. The high GST activity found in insecticide-resistant insects was associated with increased level of specific mRNA.
Glutathione S-transferases, Enzyme induction, Allelochemicals, Insecticide resistance
