Insecticides glutathione conjugation

Insects are also capable of forming glutathione conjugates, this being probably involved in the dehydrochlorination of the insecticide DDT, a reaction at least some insects, such as flies, are able to carry out (chap. 4, Fig. 42). 

The oxidation of naphthalene was one of the earliest examples of an epoxide as an intermediate in aromatic hydroxylation. As shown in Figure 7.3, the epoxide can rearrange nonenzymatically to yield predominantly 1-naphthol, or interact with the enzyme epoxide hydrolase to yield the dihydrodiol, or interact with glutathione S-transferase to yield the glutathione conjugate, which is ultimately metabolized to a mercapturic acid. These reactions are also of importance in the metabolism of other xenobiotics that contain an aromatic nucleus, such as the insecticide carbaryl and the carcinogen benzo(a)pyrene. 

Glutathione 5-transferases catalyze the reaction of electrophiles with glutathione to form thioether conjugates. Substrates include alkyl halides and organo-phosphorus insecticides. In the HPLC method of Brown et al. (1982), styrene oxide was used as the substrate and the activity was measured by the formation of conjugates between the styrene oxide and the reduced glutathione conjugates. 

MotoyamaN, Dauterman WC. 1978. Multiple forms of rat liver glutathione S-transferases Specificity for conjugation of 0-alkyl and 0-aryl groups of organophosphorus insecticides. J Agr Food Chem 26 1296-1301. 

Figure 12.63 provides another example of the diversity of metabolic processes to which pesticides are subjected after application. In the case of the carbamate insecticide carbaryl, the predominant processes are oxidation and hydrolysis, which maybe followed by conjugation of primary metabolites with glutathione. The character of metabolic transformations is closely related to the pesticide selectivity (toxicity) to target and non-target organisms. 

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