Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.7.1.4 (nitrite reductase)
1,847 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Pseudomonas aeruginosa strains deficient in the genes for cytochrome c1, a subunit of the cytochrome bc1 complex, or the tetraheme membrane protein NapC, which is similar to NirT of Pseudomonas stutzeri, were constructed and their growth was investigated. The cytochrome c1 mutant could not grow under anaerobic conditions with nitrite as an electron acceptor and did not reduce nitrite in spite of its producing active nitrite reductase. NirM (cytochrome c551) and azurin, which are the direct electron donors for nitrite reductase, were reduced by succinate in the presence of the membrane fraction from the wild-type strain as a mediator but not in the presence of that from the cytochrome c1 mutant. These results indicated that cytochrome bc1 complex was necessary for electron transfer from the membrane quinone pool to nitrite reductase. The NapC mutant grew anaerobically at the expense of nitrite, indicating that NapC was not necessary for nitrite reduction.
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PMID:Need for cytochrome bc1 complex for dissimilatory nitrite reduction of Pseudomonas aeruginosa. 1261 83

Nitric oxide (NO) is a key signaling and defense molecule in biological systems. The bactericidal effects of NO produced, for example, by macrophages are resisted by various bacterial NO-detoxifying enzymes, the best understood being the flavohemoglobins exemplified by Escherichia coli Hmp. However, many bacteria, including E. coli, are reported to produce NO by processes that are independent of denitrification in which NO is an obligatory intermediate. We demonstrate using an NO-specific electrode that E. coli cells, grown anaerobically with nitrate as terminal electron acceptor, generate significant NO on adding nitrite. The periplasmic cytochrome c nitrite reductase (Nrf) is shown, by comparing Nrf+ and Nrf- mutants, to be largely responsible for NO generation. Surprisingly, an hmp mutant did not accumulate more NO but, rather, failed to produce detectable NO. Anaerobic growth of the hmp mutant was not stimulated by nitrate, and the mutant failed to produce periplasmic cytochrome(s) c, leading to the hypothesis that accumulating NO in the absence of Hmp inactivates the global anaerobic regulator Fnr by reaction with the [4Fe-4S]2+ cluster (Cruz-Ramos, H., Crack, J., Wu, G., Hughes, M. N., Scott, C., Thomson, A. J., Green, J., and Poole, R. K. (2002) EMBO J. 21, 3235-3244). Fnr thus failed to up-regulate nitrite reductase. The model is supported by the inability of an fnr mutant to generate NO and by the restoration of NO accumulation to hmp mutants upon introducing a plasmid encoding Fnr* (D154A) known to confer activity in the presence of oxygen. A cytochrome bd-deficient mutant retained NO-generating activity. The present study reveals a critical balance between NO-generating and -detoxifying activities during anaerobic growth.
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PMID:Nitric oxide formation by Escherichia coli. Dependence on nitrite reductase, the NO-sensing regulator Fnr, and flavohemoglobin Hmp. 1278 87

Cytochromes c are typically characterized by the covalent attachment of haem to polypeptide through two thioether bonds with the cysteine residues of a Cys-Xaa-Xaa-Cys-His peptide motif. In many Gram-negative bacteria, the haem is attached to the polypeptide by the periplasmically functioning cytochrome c maturation (Ccm) proteins. Exceptionally, Hydrogenobacter thermophilus cytochrome c552 can be expressed as a stable holocytochrome both in the cytoplasm of Escherichia coli in an apparently uncatalysed reaction and also in the periplasm in a Ccm-mediated reaction. In the present study we show that a Met60-->Ala variant of c552, which does not have the usual distal methionine ligand to the haem iron of the mature cytochrome, can be made in the periplasm by the Ccm system. However, no holocytochrome could be detected when this variant was expressed cytoplasmically. These data highlight differences between the two modes of cytochrome c assembly. In addition, we report investigations of haem attachment to cytochromes altered to have the special Cys-Trp-Ser-Cys-Lys haem-binding motif, and Cys-Trp-Ser-Cys-His and Cys-Trp-Ala-Cys-His analogues, of the active-site haem of nitrite reductase NrfA.
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PMID:Variation of the axial haem ligands and haem-binding motif as a probe of the Escherichia coli c-type cytochrome maturation (Ccm) system. 1290 20

In Paracoccus denitrificans, electrons pass from the membrane-bound cytochrome bc(1) complex to the periplasmic nitrite reductase, cytochrome cd(1). The periplasmic protein cytochrome c(550) has often been implicated in this electron transfer, but its absence, as a consequence of mutation, has previously been shown to result in almost no attenuation in the ability of the nitrite reductase to function in intact cells. Here, the hypothesis that cytochrome c(550) and pseudoazurin are alternative electron carriers from the cytochrome bc(1) complex to the nitrite reductase was tested by construction of mutants of P. denitrificans that are deficient in either pseudoazurin or both pseudoazurin and cytochrome c(550). The latter organism, but not the former (which is almost indistinguishable in this respect from the wild type), grows poorly under anaerobic conditions with nitrate as an added electron acceptor and accumulates nitrite in the medium. Growth under aerobic conditions with either succinate or methanol as the carbon source is not significantly affected in mutants lacking either pseudoazurin or cytochrome c(550) or both these proteins. We concluded that pseudoazurin and cytochrome c(550) are the alternative electron mediator proteins between the cytochrome bc(1) complex and the cytochrome cd(1)-type nitrite reductase. We also concluded that expression of pseudoazurin is mainly controlled by the transcriptional activator FnrP.
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PMID:A mutant of Paracoccus denitrificans with disrupted genes coding for cytochrome c550 and pseudoazurin establishes these two proteins as the in vivo electron donors to cytochrome cd1 nitrite reductase. 1456 65

Intact cells of the denitrifying fungus Fusarium oxysporum were previously shown to catalyze codenitrification to form a hybrid nitrous oxide (N2O) species from nitrite and other nitrogen compounds such as azide and ammonia. Here we show that cytochrome P450nor can catalyze the codenitrification reaction to form N2O from nitric oxide (NO) but not nitrite, and azide or ammonia. The results show that the direct substrate of the codenitrification by intact cells should not be nitrite but NO, which is formed from nitrite by the reaction of a dissimilatory nitrite reductase.
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PMID:Nitrous oxide-forming codenitrification catalyzed by cytochrome P450nor. 1498 21

The oxidized "as isolated" form of Paracoccus pantotrophus cytochrome cd1 nitrite reductase has a bis-histidinyl coordinated c heme and a histidine/tyrosine coordinated d1 heme. This form of the enzyme has previously been shown to be kinetically incompetent. Upon reduction, the coordination of both hemes changes and the enzyme is kinetically activated. Here, we show that P. pantotrophus NapC, a tetraheme c-type cytochrome belonging to a large family of such proteins, is capable of reducing, and hence activating, "as isolated" cytochrome cd1. NapC is the first protein from P. pantotrophus identified as being capable of this activation step and, given the periplasmic co-location and co-expression of the two proteins, is a strong candidate to be a physiological activation partner.
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PMID:Paracoccus pantotrophus NapC can reductively activate cytochrome cd1 nitrite reductase. 1513 51

Escherichia coli can reduce nitrite to ammonium via a 120-kDa decaheme homodimeric periplasmic nitrite reductase (NrfA) complex. Recent structure-based spectropotentiometric studies are shedding light on the catalytic mechanism of NrfA; however, electron input into the enzyme has not been addressed biochemically. This study reports the first purification of NrfB, a novel 20-kDa pentaheme c-type cytochrome encoded by the nrfB gene that follows the nrfA gene in many bacterial nrf operons. Analyses by gel filtration demonstrated that NrfB purifies as a decaheme homodimer. Analysis of NrfB by UV-visible and magnetic circular dichroism spectroscopy demonstrates that all five NrfB ferric heme irons are low spin and are most likely coordinated by two axial histidine ligands. Spectropotentiometry revealed that the midpoint redox potentials of five ferric hemes were in the low potential range of 0 to -400 mV. Analysis by low temperature EPR spectroscopy revealed signals that arise from two classes of bis-His ligated low spin hemes, namely a rhombic trio at g(1,2,3) = 2.99, 2.27, and 1.5 that arises from two hemes in which the planes of histidine imidazole rings are near-parallel and a large g(max) signal at g = 3.57 that arises from three hemes in which the planes of the histidine imidazole rings are near-perpendicular. NrfB was also overexpressed as a recombinant protein, which had similar spectropotentiometric properties as the native protein. Reconstitution experiments demonstrated that the reduced decaheme NrfB dimer could serve as a direct electron donor to the oxidized decaheme NrfA dimer, thus forming a transient 20-heme [NrfB](2)[NrfA](2) electron transfer complex.
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PMID:Purification and spectropotentiometric characterization of Escherichia coli NrfB, a decaheme homodimer that transfers electrons to the decaheme periplasmic nitrite reductase complex. 1528 Mar 83

c-type cytochromes are characterized by covalent attachment of haem to the protein by two thioether bonds formed between the haem vinyl groups and the cysteine sulphurs in a CXXCH peptide motif. In Escherichia coli and many other Gram-negative bacteria, this post-translational haem attachment is catalysed by the Ccm (cytochrome c maturation) system. The features of the apocytochrome substrate required and recognized by the Ccm apparatus are uncertain. In the present study, we report investigations of maturation of cytochrome b562 variants containing CXXCR, CXXCK or CXXCM haem-binding motifs. None of them showed any evidence for correct maturation by the Ccm system. However, we have determined, for each variant, that the proteins (i) were expressed in large amounts, (ii) could bind haem in vivo and/or in vitro and (iii) were not degraded in the cell. Together with previous observations, these results strongly suggest that the apocytochrome substrate feature recognized by the Ccm system is simply the two cysteine residues and the histidine of the CXXCH haem-binding motif. Using the same experimental approach, we have also investigated a cytochrome b562 variant containing the special CWSCK motif that binds the active-site haem of E. coli nitrite reductase NrfA. Whereas a CWSCH analogue was matured by the Ccm apparatus in large amounts, the CWSCK form was not detectably matured either by the Ccm system or by the dedicated Nrf biogenesis proteins, implying that the substrate recognition features for haem attachment in NrfA may be more extensive than the CWSCK motif.
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PMID:The histidine of the c-type cytochrome CXXCH haem-binding motif is essential for haem attachment by the Escherichia coli cytochrome c maturation (Ccm) apparatus. 1580 11

The hyperthermophilic archaeon Pyrobaculum aerophilum used 20 mM Fe(III) citrate, 100 mM poorly crystalline Fe(III) oxide, and 10 mM KNO3 as terminal electron acceptors. The two forms of iron were reduced at different rates but with equal growth yields. The insoluble iron was reduced when segregated spatially by dialysis tubing, indicating that direct contact with the iron was not necessary for growth. When partitioned, there was no detectable Fe(III) or Fe(II) outside of the tubing after growth, suggesting that an electron shuttle, not a chelator, may be used as an extracellular mediator of iron reduction. The addition of 25 and 50% (vol vol(-1)) cell-free spent insoluble iron media to fresh media led to growth without a lag phase. Liquid chromatography analysis of spent media showed that cultures grown in iron, especially insoluble iron, produced soluble extracellular compounds that were absent or less abundant in spent nitrate medium. NADH-dependent ferric reductase activity increased approximately 100-fold, while nitrate reductase activity decreased 10-fold in whole-cell extracts from iron-grown cells relative to those from nitrate-grown cells, suggesting that dissimilatory iron reduction was regulated. A novel 2,6-anthrahydroquinone disulfonate oxidase activity was more than 580-fold higher in iron-grown cells than in nitrate-grown cells. The activity was primarily (>95%) associated with the membrane cellular fraction, but its physiological function is unknown. Nitrate-grown cultures produced two membrane-bound, c-type cytochromes that are predicted to be monoheme and part of nitrite reductase and a bc1 complex using genome analyses. Only one cytochrome was present in cells grown on Fe(III) citrate whose relative abundance was unchanged.
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PMID:Characterization of dissimilatory Fe(III) versus NO3- reduction in the hyperthermophilic archaeon Pyrobaculum aerophilum. 1638 43

The ability of Neisseria meningitidis to utilize both oxygen and nitrogen oxides as respiratory substrates allows it to thrive in the diverse environment of the human host. Genome analysis highlighted genes encoding a cbb(3) cytochrome oxidase, the aniA nitrite reductase gene and the norB nitric oxide reductase gene. In the present study, we used myxothiazol as an inhibitor of the bc(1) complex in intact cells and demonstrated that electron flow to nitrite reductase and the cytochrome oxidase, but not NO reductase, passes via the cytochrome bc(1) complex. UV-visible spectrophotometry of intact cells demonstrated that oxygen oxidizes c-type and b-type cytochromes. Oxidation of cytochromes by nitrite was only seen in microaerobically precultured whole cells, and the predominant oxidizable cytochromes were b-type. These are likely to be associated with the oxidation of a b-haem-containing nitric oxide reductase. Nitrite inhibits the oxidation of cytochromes by oxygen in a nitrite reductase-independent manner, indicating that nitrite may inhibit oxidase activity directly, as well as via the intermediate of denitrification, nitric oxide.
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PMID:Organization of the respiratory chain of Neisseria meningitidis. 1641 4


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