Chlorpyrifos-oxon hydrolysis

Figure 2 Hydrolysis of chlorpyrifos oxon by A-esterase. Although water is also involved in the reaction, it is usually ignored because it is present at an extremely high and constant concentration.

FIG. 2, Schematic illustrating the interaction of acetj Icholine (I), the carbamate carbaryl (II), and the organophosphate ehiorpynfos-oxon (IJI) with the active site of acetylcholinesterase (ACbE). The general rate of bound AChE hydrolysis is ACh > > carbaryl > chlorpyrifos-oxon. 

Furlong. C- E, Richter, R. J.. Seidel. S. L., and Molulsky, A. G. (1988). Role of genetic polymorphism of human plasma paraoxonaseJarylcstcrasc in hydrolysis of the in.scciicide metabolites chlorpyrifos oxon and paraoxon. Am. J. Hum. Genet. 43, 230-238. 

The results of these experiments in PONl knockout mice prompted a reexamination of the tVr vitro catalytic efficiencies of the two human PON 1 alloforms under more physiological salt concentrations (lower NaCl concentration). Results from kinetic analysis of substrate hydrolysis by purified human alloforms provided an explanation for the in v ivo finding. In the case of chlorpyrifos-oxon, the catalytic efficiency of both PONl alloforms was very high, and it was higher for the PON1rhj2 alloform (Table 1). Catalytic efficiency was still high in the case of diazoxon,... 

Smolen, J. M., and A. T. Stone, Metal(hydr)oxide surface catalyzed hydrolysis of chlorpyrifos-methyl, chlorpyrifos-methyl oxon, and paraoxon , Soil Sci. Am. J., 62, 636-643 (1997b). 

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