Transferases glutathione activity, insects

Wadleigh RW, Yu SJ (1987) Glutathione transferase activity of fall armyworm larvae toward alpha-, beta-unsaturated carbonyl allelochemicals and its induction by allelochemicals. Insect Biochem 17 759-764... 

The well-known selectivities of some organophosphates may be explained by the balance of enzymatic events. The reduced toxicity of the insecticide malathion to mammals is largely the result of rapid activation by desulfuration in the insect and the more rapid detoxificaton by carboxylesterases and glutathione transferases in the mammal (3). Design of new pest bioregulators should exploit enhanced activation and decreased detoxification capabilities in the targeted pests. 

Detoxification enzymes such as cytochrome P450 monooxygenases, glutathione S-transferases, and hydrolases play important roles in the metabolism of and resistance to insecticides in insects. These enzymes possess the capacity for rapid increases in activity in response to chemical stress, a phenomenon known as enzyme induction. Readers are referred to reviews by Terriere and Yu (1974), Terriere (1984), Brattsten (1979), Yu (1986a, 1996, 2001) and Feyereisen (2005) for discussion of work pertaining to induction of detoxification enzymes in insects. 

Even a rather simple insecticide such as methyl parathion is transformed by insects in a complex manner. The parent insecticide is activated to methyl paraoxon, which is a more potent inhibitor of the target, acetylcholinesterase in the nerve (Figure 1). This activating desulfuration is catalyzed by monooxygenases. Both the parent and the oxon are subject to detoxication by monooxygenase and glutathione transferase, while the oxon is also more labile to hydrolysis. 

Dimethoate is split by an amidase in the mammalian liver, whereas it is activated to oxon in insects. Dimethoate may also be detoxicated by glutathione transferases or isomerized to the more toxic derivatives by heating. Demeton-S-methyl is metabolized to highly toxic compounds, such as deme-ton-S-methyl sulfoxide and sulfone in plants and animals ... 

Kirby, M.L., Ottea, J.A., 1995. Multiple mechanisms for enhancement of glutathione S-transferase activities in Spodoptera fmgiperda (Lepidoptera Noctuidae). Insect Biochem. Mol. Biol. 25, 347-353. 

Konno, Y., Shishido, T., 1992. Distribution of glutathione S-transferase activity in insect tissues. Appl. Entomol. Zool. 27, 391-397. 

Lee, K., 1991. Glutathione S-transferase activities in phytophagous insects induction and inhibition by plant phototoxins and phenols. Insect Biochem. 21, 353-361. 

As reported by Russel et al., carried out metabolic smdies showed that pyrethroids are mainly metabolized by oxidation and ester cleavage, which are mediated by cytochrome isoforms and carboxylesterases, respectively (Russel et al. 2011). The biodegradation of synthetic pyrethroids is involved in the resistance of insects, in addition carboxylesterases, cytochromes P450 (CYPs) and GSTs (glutathione-5 -transferases) have all been implicated in this resistance. Intense bands of carboxy-lesterase activity in nondenaturing polyacrylamide gel had been associated with resistance to synthetic pyrethroids in various species, however, resistance... 

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