Nitrophenol reductase

Knowledge of the enzymes used by microorganisms in the transformation of nitroaromatic compounds is limited. Blasco Castillo (1993) characterized an inducible nitrophenol reductase from Rhodobacter capsulatus that catalyzed the reduction of 2,4-dinitrophenol (DNP) to 2-amino-4-nitrophenol. This enzyme was a dimer that contained flavin mononucleotide and possibly nonheme iron as... 

Blasco, R. Castillo, F. (1993)- Characterization of a nitrophenol reductase from the photot rophic bacterium Rhodoboctercapsulotus E1 FI. Applied and Environmental Microbiology, 59, 1774-8. 

Recently Blasco and Castillo (4) reported the characterization of a nitrophenol nitroreductase purified from Rhodobacter capsulatus. It is a soluble, FMN-containing flavoprotein that uses NAD(P)H as electron donor, and reduces 2,4-dinitrophenol to 2-amino-4-nitrophenol which is not further metabolized (Fig. 4). The native enzyme is a homodimer of 54 kDa. The inhibition of enzymatic activity by metal chelators, salicylhy-droxamate, /7-hydroxymercuribenzoate and Cu indicates the importance of sulfhydryl groups in the stability and/or activity of the protein, and the possible involvement of non-heme iron in reductase activity. Nitrophenol reductase activity was induced by a variety of nitrophenols, but not by other nitroaromatic compounds. However, its induction was suppressed by the inclusion of ammonium in the medium, and its role in the cell is not clear. 

Blasco, R., and F. Castillo. 1993. Characterization of a nitrophenol reductase from the phototrophic bacterium Rhodobacter capsulatus EIFI. Appl. Environ. Microbiol. 59 1774-1778. 

It has been shown that some reductases can mediate the reduction of nitro groups and of the ring to Meisenheimer-type complexes that are analogous to those that have been observed in nitrophenols (which are described later) ... 

Kadiyala and Spain 1998), 4-nitrophenol degradation involves initial hydroxylation to 4-nitrocatechol followed by elimination of nitrite with the formation of benzene-l,2,4-triol before ring fission to P-ketoadipate. In B. sphaericus, the first two reactions are carried out by a single two-component enzyme composed of a flavoprotein reductase and an oxygenase. 

Most studies in the microbial metabolism of nitroaromatic compounds used aerobic microorganisms. In most cases no mineralization of nitroaromatics occurs, and only superficial modifications of the structures are reported. However, under anaerobic sulfate-reducing conditions, the nitroaromatic compounds reportedly undergo a series of reductions with the formation of amino compounds. For example, trinitrotoluene under sulfate-reducing conditions is reduced to triaminotoluene by the enzyme nitrite reductase, which is commonly found in many Desulfovibrio spp. The removal of ammonia from triaminotoluene is achieved by reductive deamination catalyzed by the enzyme reductive deaminase, with the production of ammonia and toluene. Some sulfate reducers can metabolize toluene to (X) sub 2. Similar metabolic processes could be applied to other nitroaromatic compounds like nitrobenzene, nitrobenzoic acids, nitrophenols, and aniline. Many methanogenic bacteria can reduce nitroaromatic compounds to amino compounds. 

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