Desmethyl-parathion-methyl

The reactions show some typical oxidations of insecticides catalyzed by CYP enzymes. Carbofuran is hydroxylated to another active compound carbaryl is demethylated or hydroxylated and aldrin is epoxidated to diel-drin, which also has insecticidal properties. Phosphorothionates must be oxidized to the phosphates by CYP enzymes in order to become inhibitors of acetyl cholinesterase. Parathion-methyl is transformed to the oxon analogue, paraoxon-methyl, which is the toxic compound. It also can be demethylated to the inactive desmethyl-parathion-methyl. 

In a study of the metabolism of methyl parathion in intact and subcellular fractions of isolated rat hepatocytes, a high performance liquid chromatography (HPLC) method has been developed that separates and quantitates methyl parathion and six of its hepatic biotransformation products (Anderson et al. 1992). The six biotransformation products identified are methyl paraoxon, desmethyl parathion, desmethyl paraoxon, 4-nitrophenol, />nitrophenyl glucuronide, and /wiitrophenyl sulfate. This method is not an EPA or other standardized method, and thus it has not been included in Table 7-1. 

Glutathione S-transferases are important in the metabolism of organophosphorus insecticides resulting in detoxification. For example, methyl parathion is dealkylated by glutathione S-transferase to form desmethyl parathion and methyl glutathione (Figure 8.21). 

Fukami, J., and Shishido, T., Nature of a soluble glutathione-dependent enzyme system active in cleavage of methyl parathion to desmethyl parathion, J. Econ. Entomol., 59, 1338-1346, 1966. 

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