An NfsA Subgroup enzyme represents the major nitroreductase activity in E. coli. Enzymes from this subgroup typically use NADPH as an electron donor and reduce a wide range of substrates including nitroaromatics, quinones, flavins, and metals.
Bryant, D. W., McCalla, D. R., Leeksma, M. & Laneuville, P.
Type I nitroreductases of Escherichia coli.
▸ Abstract
Analysis of partially purified crude extract of Escherichia coli K12 by chromatography and gel electrophoresis has resulted in the separation of three distinct activities which catalyse the reduction of nitrofurazone (semicarbazone of 5-nitro-2-furaldehyde) in the presence of oxygen (type I nitroreductases). The major enzymatic activity (type IA), which was dependent solely on NADPH as a cofactor, was absent from nitrofurazone-resistant strains NFR 402 and NFR 502, but present in SIL 41, a strain which is only marginally resistant to the nitrofuran. The remaining nitroreductase activities (IB1 and IB2) utilize either NADH or NADPH as a cofactor. These activities coelute from DEAE-cellulose at pH 7.2, but may be differentiated by their behaviour on CM-cellulose at pH 5.8. The reductase activity missing in SIL 41 was observed in extracts of strain NFR 402 but not NFR 502. This enzyme (IB1) though retained by DEAE-cellulose had no affinity for CM-cellulose. The only reductase present in extracts of NFR 502 (a nitrofuran-resistant strain selected after two mutational events) was type IB2. This activity, also detectable in SIL 41 and NFR 402, has not been mapped genetically. An interesting feature of the type IB2 enzyme is its apparent inactivation by MnCl2 which has been routinely used as a partial purification step in the past.
Can. J. Microbiol.
1981;27(None):81-86
| PubMed ID:
7011517
Roldán, M. D., Pérez-Reinado, E., Castillo, F. & Moreno-Vivián, C.
Reduction of polynitroaromatic compounds: the bacterial nitroreductases.
▸ Abstract
Most nitroaromatic compounds are toxic and mutagenic for living organisms, but some microorganisms have developed oxidative or reductive pathways to degrade or transform these compounds. Reductive pathways are based either on the reduction of the aromatic ring by hydride additions or on the reduction of the nitro groups to hydroxylamino and/or amino derivatives. Bacterial nitroreductases are flavoenzymes that catalyze the NAD(P)H-dependent reduction of the nitro groups on nitroaromatic and nitroheterocyclic compounds. Nitroreductases have raised a great interest due to their potential applications in bioremediation, biocatalysis, and biomedicine, especially in prodrug activation for chemotherapeutic cancer treatments. Different bacterial nitroreductases have been purified and their biochemical and kinetic parameters have been determined. The crystal structure of some nitroreductases have also been solved. However, the physiological role(s) of these enzymes remains unclear. Nitroreductase genes are widely spread within bacterial genomes, but are also found in archaea and some eukaryotic species. Although studies on regulation of nitroreductase gene expression are scarce, it seems that nitroreductase genes may be controlled by the MarRA and SoxRS regulatory systems that are involved in responses to several antibiotics and environmental chemical hazards and to specific oxidative stress conditions. This review covers the microbial distribution, types, biochemical properties, structure and regulation of the bacterial nitroreductases. The possible physiological functions and the biotechnological applications of these enzymes are also discussed.
FEMS Microbiol Rev
2008;32(None):474-500
| PubMed ID:
18355273
McCalla, D. R., Kaiser, C. & Green, M. H.
Genetics of nitrofurazone resistance in Escherichia coli.
▸ Abstract
Wild-type Escherichia coli cells are sensitive to nitrofurazone (NF) and many other nitrofuran derivatives. A variety of evidence indicated that these compounds are converted to toxic "active" metabolites by reductases present in the bacteria. Sensitive E. coli K-12 acquired threefold-greater resistance to NF in one mutational step. These partially resistant mutants could undergo a second mutation that made them 10 times as resistant as the wild type. Mutation of wild-type strain K-12 to the higher level of resistance in a single step was not observed. The first mutational step was associated with partial loss of reduced nicotinamide adenine dinucleotide phosphate-linked, O(2)-insensitive NF reductase activity, and the second step was associated with loss of the remaining activity. The two-step mutants did, however, contain other NF reductases that were inhibited by O(2) and reduced NF only under anaerobic conditions. We designated the genes that control reductase activity "nitrofuran sensitivity genes" (nfsA and nfsB). Thus, wild-type strains are nfsA(+)nfsB(+), and the resistant double mutants are nfsA nfsB. A variety of crosses established that these genes are both located close to gal, that the most probable sequence is lac nfsB gal nfsA, and that the single-step mutants with an intermediate level of resistance are nfsA nfsB(+). The nfsA(+)nfsB strains contained about 70 to 80% of the wild-type reductase I activity-apparently enough to confer wild-type sensitivity. This reductase activity was resistant to 2 M urea. The nfsA nfsB(+) strains had only 20 to 30% of the wild-type activity, and this residual activity was sensitive to 2 M urea.
Journal of Bacteriology
1978;133(None):10-16
| PubMed ID:
338576
Zenno, S. et al.
Biochemical characterization of NfsA, the Escherichia coli major nitroreductase exhibiting a high amino acid sequence homology to Frp, a Vibrio harveyi flavin oxidoreductase.
▸ Abstract
We identified the nfsA gene, encoding the major oxygen-insensitive nitroreductase in Escherichia coli, and determined its position on the E. coli map to be 19 min. We also purified its gene product, NfsA, to homogeneity. It was suggested that NfsA is a nonglobular protein with a molecular weight of 26,799 and is associated tightly with a flavin mononucleotide. Its amino acid sequence is highly similar to that of Frp, a flavin oxidoreductase from Vibrio harveyi (B. Lei, M. Liu, S. Huang, and S.-C. Tu, J. Bacteriol. 176:3552-3558, 1994), an observation supporting the notion that E. coli nitroreductase and luminescent-bacterium flavin reductase families are intimately related in evolution. Although no appreciable sequence similarity was detected between two E. coli nitroreductases, NfsA and NfsB, NfsA exhibited a low level of the flavin reductase activity and a broad electron acceptor specificity similar to those of NfsB. NfsA reduced nitrofurazone by a ping-pong Bi-Bi mechanism possibly to generate a two-electron transfer product.
Journal of Bacteriology
1996;178(None):4508-4514
| PubMed ID:
8755878
