Optimization of reaction time for detection of organophosphorus pesticides by enzymatic inhibition assay and mathematical modeling of enzyme inhibition.

Enzyme inhibition assay was used as a biomarker for detection of organophosphates pesticides in food and environmental samples. The aim of the present study was to optimize the time of enzyme-inhibitor reaction for quantitative determination of fenitrothion organophosphate based on cholinesterase inhibition. The results showed that this method provides a time-efficient, best linearity and simple assay. The effect of reaction time on the linearity relationship of the noncompetitive inhibition equation was studied. The best linearity of the assay was found at an optimum reaction time of 3.0 min, with coefficient of determination of 0.9972, in the range of inhibitor concentrations from 0.016 to 2.0 μg mL. The enzyme inhibition reached a plateau at 5 min by addition of pesticide in vitro and then the inhibited enzyme reactivate spontaneously and approached steady state at 20 min. A theoretical kinetic model to explain the effect of reaction time on the enzyme inhibition by addition of pesticide in vitro was derived. The higher values of coefficient of determination for the predicted model and error functions of the minimum deviations suggest that this model can be used to represent the experimental data and explain the plasma cholinesterase inhibition by fenitrothion pesticide.