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Published on: September 7, 2015
[Lipoxygenase-mediated N-demethylation of pesticides in vitro]
1Department of Occupational Medicine, School of Public Health, Central South University, Changsha 410078, China.
Objective:
In order to explore the pathway of dealkylation of pesticides other than cytochrome P450 monocoxygenases, lipoxygenase (LOX)-mediated demethylation of aminocarb and some other pesticides were measured.
Method:
Formaldehyde generated in the reaction was estimated by Nash reaction to express the rate of demethylation of pesticides mediated by soy lipoxygenase (SLO).
Results:
N-demethylation of aminocarb mediated by SLO was found to depend on the incubation time, concentration of the enzyme, concentration of aminocarb and hydrogen peroxide. Under optimal conditions, Vmax value of 18 nmol of formaldehyde.min-1.nmol-1 of lipoxygenase was observed. The reaction exhibited Km values of 3.4 mmol/L for aminocarb and 235 mumol/L for hydrogen peroxide. A strong inhibition of the reaction by nordihydroguaiaretic acid, gossypol, and phenidone clearly implicated the lipoxygenase involvement as the protein catalyst. A significant decline in the formaldehyde accumulation in the presence of either reduced glutathione or dithiothreitol suggested generation of a free radical species as an initial oxidation intermediate during the demethylation of aminocarb by SLO. The inhibition of formaldehyde generation by butylated hydroxyanisole(BHT) and butylated hydroxy toluene(BHA) further supported this contention. In addition to aminocarb, seven other pesticides were also found to undergo N-demethylation, albeit at relatively low rates.
Conclusion:
Certain pesticides may oxidatively undergo dealkylation via the lipoxygenase pathway in animals and plants.
