Lipoxygenase-mediated hydrogen peroxide-dependent N-demethylation of N, N-dimethylaniline and related compounds

Abstract

To date, studies of xenobiotic N-demethylation have focused on heme-proteins such as P-450 and peroxidases. In this study we investigated the ability of non-heme iron proteins, namely soybean lipoxygenase (SLO) and human term placental lipoxygenase (HTPLO) to mediate N-demethylation of N, N-dimethylaniline (DMA) and related compounds in the presence of hydrogen peroxide. In addition to being hydrogen peroxide dependent, the reaction was also dependent on incubation time, concentration of enzyme and DMA and the pH of the medium. Using Nash reagent to estimate formaldehyde production, we determined the specific activity for SLO mediated N-demethylation of DMA to be 200±18 nmol HCHO/min per mg protein or 23±2 nmol/min per nmol of enzyme, while that of HTPLO was 33±4 nmol HCHO/min per mg protein. Nordihydroguaiaretic acid (NDGA), a classical inhibitor of lipoxygenase (LO), as well as antioxidants and free radical reducing agents, caused a marked reduction in the rate of production of formaldehyde from DMA by SLO. Besides N, N-dimethylaniline, N-methylaniline, N, N, N′, N′-tetramethylbenzidine, N, N-dimethyl- p-phenylenediamine, N, N-dimethyl-3-nitroaniline and N, N-dimethyl- p-toluidine were also demethylated by SLO. The formation of a DMA N-oxide was not detected. Preliminary experiments suggested SLO-mediated hydrogen peroxide-dependent S-dealkylation of methiocarb or O-dealkylation of 4-nitroanisole does not occur.