Converging catabolism of 2,4,6-trinitrophenol (picric acid) and 2,4-dinitrophenol by Nocardioides simplex FJ2-1A

Initial F420-dependent hydrogenation of 2,4,6-trinitrophenol (picric acid) generated the hydride sigma-complex of picrate and finally the dihydride complex. With 2,4-dinitrophenol the hydride sigma-complex of 2,4-dinitrophenol is generated. The hydride transferring enzyme system showed activity against several substituted 2,4-dinitrophenols but not with mononitrophenols. A Km-value of 0.06 mM of the hydride transfer for picrate as substrate was found. The pH optima of the NADPH-dependent F420 reductase and for the hydride transferase were 5.5 and 7.5, respectively. An enzymatic activity has been identified catalyzing the release of stoichometric amounts of 1 mol nitrite from 1 mol of the dihydride sigma-complex of picrate. This complex was synthesized by chemical reduction of picrate and characterized by 1H and 13C NMR spectroscopy. The hydride sigma-complex of 2,4-dinitrophenol has been identified as the denitration product. The nitrite-eliminating activity was enriched and clearly separated from the hydride transferring enzyme system by FPLC. 2,4-Dinitrophenol has been disproven as a metabolite of picrate (Ebert et al. 1999) and a convergent catabolic pathway for picrate and 2,4-dinitrophenol with the hydride sigma-complex of 2,4-dinitrophenol as the common intermediate has been demonstrated.