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Query: EC:1.7.1.1 (nitrate reductase)
3,728 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The phototrophic bacterium Rhodobacter sphaeroides DSM 158 has a periplasmic nitrate reductase which is induced by nitrate and it is not repressed by ammonium or oxygen. In a Tn5 mutant lacking nitrate reductase activity, transposon insertion is localized in a 1.2 kb EcoRI fragment. A 0.6 kb BamHI-EcoRI segment of this region was used as a probe to isolate, from the wild-type strain, a 6.8 kb PstI fragment carrying the putative genes coding for the periplasmic nitrate reductase. In vivo protein expression and DNA sequence analysis reveal the presence in this region of three genes, napABC, probably organized in an operon. These genes are required for nitrate reduction, as deduced by mutational and complementation studies. The napA gene codes for a protein with a high homology to the periplasmic nitrate reductase from Alcaligenes eutrophus and, to a lesser extent, to other prokaryotic nitrate reductases and molybdenum-containing enzymes. The napB gene product has two haem c-binding sites and shows a high homology with the cytochrome c-type subunit of the periplasmic nitrate reductase from A. eutrophus. NAPA and NAPB proteins appear to be translated with signal peptides of 29 and 24 residues, respectively, indicating that mature proteins are located in the periplasm. The napC gene codes for a 25 kDa protein with a transmembrane sequence of 17 hydrophobic residues. NAPC has four haem c-binding sites and is homologous to the membrane-bound c-type cytochromes encoded by Pseudomonas stutzeri nirT and Escherichia coli torC genes. The phenotypes of defined insertion mutants constructed for each gene also indicate that periplasmic nitrate reductase from R. sphaeroides DSM 158 is a dimeric complex of a 90 kDa catalytic subunit (NAPA) and a 15 kDa cytochrome c (NAPB), which receives electrons from a membrane-anchored tetrahaem protein (NAPC), thus allowing electron flow between membrane and periplasm. This nitrate-reducing system differs from the assimilatory and respiratory bacterial nitrate reductases at the level of cellular localization, regulatory properties, biochemical characteristics and gene organization.
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PMID:Isolation of periplasmic nitrate reductase genes from Rhodobacter sphaeroides DSM 158: structural and functional differences among prokaryotic nitrate reductases. 873 Aug 72

The 'aeg46.5' operon was originally detected as an 'anaerobically expressed gene' located at minute 46.5 on the Escherichia coli linkage map. Subsequent results from the E. coli Genome Sequencing Project revealed that the 'aeg46.5' promoter was located in the centisome 49 (minute 47) region. Downstream from this promoter are 15 genes, seven of which are predicted to encode a periplasmic nitrate reductase and eight encode proteins homologous to proteins essential for cytochrome c assembly in other bacteria. All of these genes, together with the 'aeg46.5' promoter, have been subcloned on a 20kb EcoRI fragment from Kohara phage 19D1. Evidence is presented that, as predicted, the region includes structural genes for two c-type cytochromes of mass 16kDa and 24 kDa, which are transcribed from the previously described 'aeg46.5' promoter, and that the first seven genes encode a functional nitrate reductase. We, therefore, propose that they should be designated nap (nitrate reductase in the periplasm) genes. Plasmids encoding the entire 20kb region, or only the downstream eight genes, complemented five mutations resulting in total absence of all five known c-type cytochromes in E coli, providing biochemical evidence that these are ccm (for cytochrome c maturation) genes. The ccm region was transcribed both from the FNR-dependent, NarL- and NarP-regulated nap promoter (formerly the 'aeg46.5' promoter) and from constitutive or weakly regulated promoters apparently located within the downstream nap and ccm genes.
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PMID:Escherichia coli K-12 genes essential for the synthesis of c-type cytochromes and a third nitrate reductase located in the periplasm. 883 Feb 38

The assembly of anaerobically induced electron transfer chains in Escherichia coli strains defective in periplasmic disulphide bond formation was investigated. Strains deficient in DsbA, DsbB or DipZ (DsbD) were unable to catalyse formate-dependent nitrite reduction (Nrf activity) or synthesize any of the known c-type cytochromes. The Nrf+ activity and cytochrome c content of mutants defective in DsbC, DsbE or DsbF were similar to those of the parental, wild-type strain. Neither DsbC expressed from a multicopy plasmid nor a second mutation in dipZ (dsbD) was able to compensate for a dsbA mutation by restoring nitrite reductase activity and cytochrome c synthesis. In contrast, only the dsbB and dipZ (dsbD) strains were defective in periplasmic nitrate reductase activity, suggesting that DsbB might fulfil an additional role in anaerobic electron transport. Mutants defective in dipZ (dsbD) were only slightly more sensitive to Cu++ ions at concentrations above 5 mM than the parental strain, but strains defective in DsbA, DsbB, DsbC, DsbE or DsbF were unaffected. These results are consistent with our earlier proposals that DsbA, DsbB and DipZ (DsbD) are part of the same pathway for ensuring that haem groups are attached to the correct pairs of cysteine residues of apocytochromes c in the E. coli periplasm. However, neither DsbE nor DsbF are essential for the reduction of DipZ (DsbD).
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PMID:Effects of mutations in genes for proteins involved in disulphide bond formation in the periplasm on the activities of anaerobically induced electron transfer chains in Escherichia coli K12. 900 92

A 13-kb genomic region of Paracoccus dentrificans GB17 is involved in lithotrophic thiosulfate oxidation. Adjacent to the previously reported soxB gene (C. Wodara, S. Kostka, M. Egert, D. P. Kelly, and C. G. Friedrich, J. Bacteriol. 176:6188-6191, 1994), 3.7 kb were sequenced. Sequence analysis revealed four additional open reading frames, soxCDEF. soxC coded for a 430-amino-acid polypeptide with an Mr of 47,339 that included a putative signal peptide of 40 amino acids (Mr of 3,599) with a RR motif present in periplasmic proteins with complex redox centers. The mature soxC gene product exhibited high amino acid sequence similarity to the eukaryotic molybdoenzyme sulfite oxidase and to nitrate reductase. We constructed a mutant, GBsoxC delta, carrying an in-frame deletion in soxC which covered a region possibly coding for the molybdenum cofactor binding domain. GBsoxC delta was unable to grow lithoautotrophically with thiosulfate but grew well with nitrate as a nitrogen source or as an electron acceptor. Whole cells and cell extracts of mutant GBsoxC delta contained 10% of the thiosulfate-oxidizing activity of the wild type. Only a marginal rate of sulfite-dependent cytochrome c reduction was observed from cell extracts of mutant GBsoxC delta. These results demonstrated that sulfite dehydrogenase was essential for growth with thiosulfate of P. dentrificans GB17. soxD coded for a periplasmic diheme c-type cytochrome of 384 amino acids (Mr of 39,983) containing a putative signal peptide with an Mr of 2,363. soxE coded for a periplasmic monoheme c-type cytochrome of 236 amino acids (Mr of 25,926) containing a putative signal peptide with an Mr of 1,833. SoxD and SoxE were highly identical to c-type cytochromes of P. denitrificans and other organisms. soxF revealed an incomplete open reading frame coding for a peptide of 247 amino acids with a putative signal peptide (Mr of 2,629). The deduced amino acid sequence of soxF was 47% identical and 70% similar to the sequence of the flavoprotein of flavocytochrome c of Chromatium vinosum, suggesting the involvement of the flavoprotein in thiosulfate oxidation of P. denitrificans GB17.
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PMID:Cloning and characterization of sulfite dehydrogenase, two c-type cytochromes, and a flavoprotein of Paracoccus denitrificans GB17: essential role of sulfite dehydrogenase in lithotrophic sulfur oxidation. 926 Sep 41

The assimilatory nitrate reductase from the phototrophic bacterium Rhodobacter capsulatus has been purified to electrophoretic homogeneity and its molecular and kinetic parameters determined. The native nitrate reductase is a dimer of 144 kDa composed of two subunits of 46 and 95 kDa. The purified enzyme catalyzes the electron transfer from NADH, reduced bromophenol blue or reduced viologens to nitrate. The nitrate reductase contains 1 mol FAD per mole of enzyme and also reduces cytochrome c or dichlorophenol indophenol with NADH as the electron donor. The diaphorase activity is located in the small subunit.
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PMID:The assimilatory nitrate reductase from the phototrophic bacterium, Rhodobacter capsulatus E1F1, is a flavoprotein. 930 29

Three Escherichia coli mutants defective in formate-dependent nitrite reduction (Nrf activity) were characterised. Two of the mutants, JCB354 and JCB356, synthesized all five c-type cytochromes previously characterised in anaerobic cultures of E. coli. The third mutant, JCB355, was defective for both cytochrome b and cytochrome c synthesis, but only during anaerobic growth. The insertion sites of the transposon in strains JCB354 and JCB356 mapped to the menFDBCE operon; the hemN gene was disrupted in strain JCB355. The mutation in strain JCB354 was complemented by a plasmid encoding only menD; strain JCB356 was complemented by a plasmid encoding only menBCE. A mutant defective in the methyltransferase activity involved in both ubiquinone synthesis and conversion of demethylmenaquinone to menaquinone expressed the same Nrf activity as the parental strain. The effects of men, ubiA and ubiE mutations on other cytochrome-c-dependent electron transfer pathways were also determined. The combined data establish that menaquinones are essential for cytochrome-c-dependent trimethylamine-N-oxide reductase (Tor) and Nrf activity, but that either menaquinone or ubiquinone, but not demethylmenaquinone, can transfer electrons to a third cytochrome-c-dependent electron transfer chain, the periplasmic nitrate reductase.
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PMID:Characterisation of Escherichia coli K-12 mutants defective in formate-dependent nitrite reduction: essential roles for hemN and the menFDBCE operon. 932 29

The eight ccm genes located at minute 47 on the Escherichia coli chromosome, in the order ccmABCDEFGH, encode homologues of proteins which are essential for cytochrome c assembly in other bacteria. The ccm genes are immediately downstream from the napFDAGHBC genes encoding a periplasmic nitrate reductase. CcmH was previously shown to be essential for cytochrome c assembly. Deletion analysis and a two-plasmid strategy have now been used to demonstrate that CcmA, B, D, E, F and G are also essential for cytochrome c assembly, and hence for cytochrome-c-dependent nitrite reduction. The ccm genes are transcribed from a ccmA promoter located within the adjacent gene, napC, which is the structural gene for a 24 kDa membrane-bound c-type cytochrome, NapC. Transcription from this ccmA promoter is induced approximately 5-fold during anaerobic growth, independently of a functional Fnr protein: it is also not regulated by the ArcB-ArcA two-component regulatory system. The ccmA promoter is an example of the 'extended -10 sequence' group of promoters with a TGX motif immediately upstream of the -10 sequence. Mutagenesis of the TG motif to TC, CT or CC resulted in loss of about 50% of the promoter activity. A weak second promoter is suggested to permit transcription of the downstream ccmEFGH genes in the absence of transcription readthrough from the upstream napF and ccmA promoters. The results are consistent with, but do not prove, the current view that CcmA, B, C and D are part of an essential haem transport mechanism, that CcmE, F and H are required for covalent haem attachment to cysteine-histidine motifs in cytochrome c apoproteins in the periplasm, and that CcmG is required for the reduction of cysteine residues on apocytochromes c in preparation for haem ligation.
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PMID:Transcriptional control and essential roles of the Escherichia coli ccm gene products in formate-dependent nitrite reduction and cytochrome c synthesis. 971 93

Escherichia coli synthesizes two biochemically distinct nitrate reductase enzymes, a membrane-bound enzyme encoded by the narGHJI operon and a periplasmic cytochrome c-linked nitrate reductase encoded by the napFDAGHBC operon. To address why the cell makes these two enzymes, continuous cell culture techniques were used to examine napF and narG gene expression in response to different concentrations of nitrate and/or nitrite. Expression of the napF-lacZ and narG-lacZ reporter fusions in strains grown at different steady-state levels of nitrate revealed that the two nitrate reductase operons are differentially expressed in a complementary pattern. The napF operon apparently encodes a "low-substrate-induced" reductase that is maximally expressed only at low levels of nitrate. Expression is suppressed under high-nitrate conditions. In contrast, the narGHJI operon is only weakly expressed at low nitrate levels but is maximally expressed when nitrate is elevated. The narGHJI operon is therefore a "high-substrate-induced" operon that somehow provides a second and distinct role in nitrate metabolism by the cell. Interestingly, nitrite, the end product of each enzyme, had only a minor effect on the expression of either operon. Finally, nitrate, but not nitrite, was essential for repression of napF gene expression. These studies reveal that nitrate rather than nitrite is the primary signal that controls the expression of these two nitrate reductase operons in a differential and complementary fashion. In light of these findings, prior models for the roles of nitrate and nitrite in control of narG and napF expression must be reconsidered.
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PMID:The napF and narG nitrate reductase operons in Escherichia coli are differentially expressed in response to submicromolar concentrations of nitrate but not nitrite. 1046 1

The combined action of ammonia monooxygenase, AMO, (NH(3)+2e(-)+O(2)-->NH(2)OH) and hydroxylamine oxidoreductase, HAO, (NH(2)OH+H(2)O-->HNO(2)+4e(-)+4H(+)) accounts for ammonia oxidation in Nitrosomonas europaea. Pathways for electrons from HAO to O(2), nitrite, NO, H(2)O(2) or AMO are reviewed and some recent advances described. The membrane cytochrome c(M)552 is proposed to participate in the path between HAO and ubiquinone. A bc(1) complex is shown to mediate between ubiquinol and the terminal oxidase and is shown to be downstream of HAO. A novel, red, low-potential, periplasmic copper protein, nitrosocyanin, is introduced. Possible mechanisms for the inhibition of ammonia oxidation in cells by protonophores are summarized. Genes for nitrite- and NO-reductase but not N(2)O or nitrate reductase are present in the genome of Nitrosomonas. Nitrite reductase is not repressed by growth on O(2); the flux of nitrite reduction is controlled at the substrate level.
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PMID:Electron transfer during the oxidation of ammonia by the chemolithotrophic bacterium Nitrosomonas europaea. 1100 50

The napB gene of the pathogenic bacterium Haemophilus influenzae encodes a dihaem cytochrome c, the small subunit of a heterodimeric periplasmic nitrate reductase (Nap). Recombinant NapB was overproduced in Escherichia coli, purified to near-homogeneity and crystallized using the hanging-drop method. Thin quadrilateral plates were grown under various conditions but proved to be unsuitable for X-ray analysis. However, a single crystal was grown using 1.75 M ammonium sulfate in 0.1 M sodium acetate pH 5.5, from which a native data set could be collected to 1.8 A resolution using synchrotron radiation. Using the same conditions, further crystals were obtained by microseeding. The space group was determined to be P42(1)2, with unit-cell parameters a = 77.55, b = 77.55, c = 28.64 A and an unusually low solvent content of 16.5%, assuming there to be one molecule of NapB in the asymmetric unit. Analysis of the dissolved crystals indicated that partial proteolysis of the protein had occurred. Taking the molecular mass of the crystallized form ( approximately 8500 Da) into account, the solvent content was estimated to be 53%, with a V(M) value of 2.64 A(3) Da(-1).
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PMID:Crystallization and preliminary X-ray analysis of the recombinant dihaem cytochrome c (NapB) from Haemophilus influenzae. 1122 19


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