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Query: EC:1.7.1.2 (nitrate reductase)
 3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Heterotrophic nitrification and aerobic and anaerobic denitrification by Alcaligenes faecalis strain TUD were studied in continuous cultures under various environmental conditions. Both nitrification and denitrification activities increased with the dilution rate. At dissolved oxygen concentrations above 46% air saturation, hydroxylamine, nitrite and nitrate accumulated, indicating that both the nitrification and denitrification were less efficient. The overall nitrification activity was, however, essentially unaffected by the oxygen concentration. The nitrification rate increased with increasing ammonia concentration, but was lower in the presence of nitrate or nitrite. When present, hydroxylamine, was nitrified preferentially. Relatively low concentrations of acetate caused substrate inhibition (KI = 109 microM acetate). Denitrifying or assimilatory nitrate reductase were not detected, and the copper nitrite reductase, rather than cytochrome cd, was present. Thiosulphate (a potential inhibitor of heterotrophic nitrification) was oxidized by A. faecalis strain TUD, with a maximum oxygen uptake rate of 140-170 nmol O2.min-1.mg prot-1. Comparison of the behaviour of A. faecalis TUD with that of other bacteria capable of heterotrophic nitrification and aerobic denitrification established that the response of these organisms to environmental parameters is not uniform. Similarities were found in their responses to dissolved oxygen concentrations, growth rate and ammonia concentration. However, they differed in their responses to externally supplied nitrite and nitrate.
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PMID:Heterotrophic nitrification and aerobic denitrification in Alcaligenes faecalis strain TUD. 141 19

An open reading frame from Rhizobium leguminosarum bv. viciae strain VF39, previously identified and found to be similar to Escherichia coli fnr and Rhizobium meliloti fixK (orf240, thereafter called fnrN), was further analysed. Analysis of the expression of an fnrN-lacZ transcriptional fusion revealed that fnrN is preferentially expressed under oxygen limitation. Using R. meliloti fixN-lacZ fusions it was shown that the fnrN gene product only mediates transcriptional activation under microaerobiosis, indicating that the FnrN protein responds, directly or indirectly, to oxygen. Plasmids which expressed fnrN under the control of an E. coli promoter were able to complement an E. coli fnr mutant with respect to anaerobic growth on nitrate but not fumarate, and to promote anaerobic but not aerobic activation of the Fnr-dependent E. coli genes narGHJI, nirB and fdnGHI coding for nitrate reductase, NADH-dependent nitrite reductase and formate dehydrogenase-N, respectively. Fumarate and DMSO reductase activities were not induced by FnrN. The E. coli fnr gene substituted for fnrN in oxygen-regulated transcription of nirB- and fixN-lacZ fusions in R. leguminosarum. The results indicate that Fnr and FnrN are functionally very similar and share a common mode of oxygen-dependent transcriptional activation. From hybridization studies, it appeared that fnrN-like genes are present in a number of different R. leguminosarum strains.
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PMID:The Rhizobium leguminosarum FnrN protein is functionally similar to Escherichia coli Fnr and promotes heterologous oxygen-dependent activation of transcription. 148 91

Transcriptional expression of the puc operon in Rhodobacter sphaeroides is highly regulated by both oxygen and light. The approximately 600 bp of DNA upstream of the 5' ends of the two puc-specific transcripts encompasses two functionally separable cis-acting domains. The upstream regulatory region (URS) (-629 to -150) is responsible for enhanced transcriptional regulation of puc operon expression by oxygen and light. The more proximal upstream region (downstream regulatory region [DRS]), containing putative promoter(s), operator(s), and factor binding sites (-150 to -1), is involved in unenhanced transcriptional expression of the puc operon under aerobic and anaerobic conditions. Thus, the DRS shows normal derepression of puc operon expression when cells are shifted from aerobic to photosynthetic growth conditions in terms of percent change but does not show the potential range of expression that is only observed when elements of the URS are present. Because of these observations, we have made a distinction between anaerobic control (describing the shift) and oxygen control (describing the magnitude of derepression). Promoter(s) and/or activator function(s) of the puc operon is associated with a 35-bp DNA region between -92 and -57. Homologous sequences at -10 to -27 and -35 to -52 appear to involve additional regulatory elements: mutations at -12 (A to C) and -26 (G to A) result in partial derepression of puc operon expression under conditions of high aeration. Both point mutations require the upstream regulatory region (-629 to -150) to be present in cis for partial derepression of puc operon transcription under aerobic conditions. Immediately upstream of the promoter and/or activator region are overlapping consensus sequences for IHF (integratin host factor) and FNR (fumarate nitrate reductase) (-105 to -129). This region appears to be essential for enhanced expression of the puc operon. Thus, these two regulatory domains (URS and DRS) appear to involve approximately seven unique regulatory elements. In addition, the data reveal a direct interaction between the URS (-629 to -150) and the DRS (-150 to -1).
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PMID:cis-acting regulatory elements involved in oxygen and light control of puc operon transcription in Rhodobacter sphaeroides. 173 9

The regulatory protein Fnr is required for anaerobic expression of several anaerobic respiratory enzymes in Escherichia coli. To gain insight into how Fnr activity is regulated by oxygen, we have isolated Fnr mutants that increase expression of the nitrate reductase operon in the presence of oxygen (Fnr* mutants). Seven single-amino-acid substitutions that mapped within two regions of Fnr have been characterized. Two mutants mapped adjacent to two Cys residues in the N-terminal Cys cluster. Five Fnr* substitutions mapped to a region of Fnr that is similar to the cyclic AMP-binding domain of the catabolite activator protein (CAP). Within this group, four mutants were clustered in a region analogous to the CAP C helix, which is important in CAP dimer subunit interactions. Taken together, these data implicate regions in Fnr that may be important either in sensing oxygen deprivation or in the conformational change proposed to be necessary for Fnr activation under anaerobic conditions.
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PMID:Fnr mutants that activate gene expression in the presence of oxygen. 189 18

A mutant of Pseudomonas aeruginosa was characterized which could not grow anaerobically with nitrate as the terminal electron acceptor or with arginine as the sole energy source. In this anr mutant, nitrate reductase and arginine deiminase were not induced by oxygen limitation. The anr mutation was mapped in the 60-min region of the P. aeruginosa chromosome. A 1.3-kb chromosomal fragment from P. aeruginosa complemented the anr mutation and also restored anaerobic growth of an Escherichia coli fnr deletion mutant on nitrate medium, indicating that the 1.3-kb fragment specifies an FNR-like regulatory protein. The arcDABC operon, which encodes the arginine deiminase pathway enzymes of P. aeruginosa, was rendered virtually noninducible by a deletion or an insertion in the -40 region of the arc promoter. This -40 sequence (TTGAC....ATCAG) strongly resembled the consensus FNR-binding site (TTGAT....ATCAA) of E. coli. The cloned arc operon was expressed at low levels in E. coli; nevertheless, some FNR-dependent anaerobic induction could be observed. An FNR-dependent E. coli promoter containing the consensus FNR-binding site was expressed well in P. aeruginosa and was regulated by oxygen limitation. These findings suggest that P. aeruginosa and E. coli have similar mechanisms of anaerobic control.
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PMID:Positive FNR-like control of anaerobic arginine degradation and nitrate respiration in Pseudomonas aeruginosa. 190 Feb 77

Pseudomonas aeruginosa is an obligate respirer which can utilize nitrate as a terminal electron acceptor under anaerobic conditions (denitrification). Immediate, transient regulation of nitrate respiration is mediated by oxygen through the inhibition of nitrate uptake. In order to gain an understanding of the bioenergetics of nitrate transport and its regulation by oxygen, the effects of various metabolic inhibitors on the uptake process and on oxygen regulation were investigated. Nitrate uptake was stimulated by the protonophores carbonyl cyanide m-chlorophenylhydrazone and 2,4-dinitrophenol, indicating that nitrate uptake is not strictly energized by, but may be affected by the proton motive force. Oxygen regulation of nitrate uptake might in part be through redox-sensitive thiol groups since N-ethylmaleimide at high concentrations decreased the rate of nitrate transport. Cells grown with tungstate (deficient in nitrate reductase activity) and azide-treated cells transported nitrate at significantly lower rates than untreated cells, indicating that physiological rates of nitrate transport are dependent on nitrate reduction. Furthermore, tungstate grown cells transported nitrate only in the presence of nitrite, lending support to the nitrate/nitrite antiport model for transport. Oxygen regulation of nitrate transport was relieved (10% that of typical anaerobic rates) by the cytochrome oxygen reductase inhibitors carbon monoxide and cyanide.
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PMID:Nitrate transport and its regulation by O2 in Pseudomonas aeruginosa. 191 Feb 83

Under anaerobic circumstances in the presence of nitrate Paracoccus denitrificans is able to denitrify. The properties of the reductases involved in nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase are described. For that purpose not only the properties of the enzymes of P. denitrificans are considered but also those from Escherichia coli, Pseudomonas aeruginosa, and Pseudomonas stutzeri. Nitrate reductase consists of three subunits: the alpha subunit contains the molybdenum cofactor, the beta subunit contains the iron sulfur clusters, and the gamma subunit is a special cytochrome b. Nitrate is reduced at the cytoplasmic side of the membrane and evidence for the presence of a nitrate-nitrite antiporter is presented. Electron flow is from ubiquinol via the specific cytochrome b to the nitrate reductase. Nitrite reductase (which is identical to cytochrome cd1) and nitrous oxide reductase are periplasmic proteins. Nitric oxide reductase is a membrane-bound enzyme. The bc1 complex is involved in electron flow to these reductases and the whole reaction takes place at the periplasmic side of the membrane. It is now firmly established that NO is an obligatory intermediate between nitrite and nitrous oxide. Nitrous oxide reductase is a multi-copper protein. A large number of genes is involved in the acquisition of molybdenum and copper, the formation of the molybdenum cofactor, and the insertion of the metals. It is estimated that at least 40 genes are involved in the process of denitrification. The control of the expression of these genes in P. denitrificans is totally unknown. As an example of such complex regulatory systems the function of the fnr, narX, and narL gene products in the expression of nitrate reductase in E. coli is described. The control of the effects of oxygen on the reduction of nitrate, nitrite, and nitrous oxide are discussed. Oxygen inhibits reduction of nitrate by prevention of nitrate uptake in the cell. In the case of nitrite and nitrous oxide a competition between reductases and oxidases for a limited supply of electrons from primary dehydrogenases seems to play an important role. Under some circumstances NO formed from nitrite may inhibit oxidases, resulting in a redistribution of electron flow from oxygen to nitrite. P. denitrificans contains three main oxidases: cytochrome aa3, cytochrome o, and cytochrome co. Cytochrome o is proton translocating and receives its electrons from ubiquinol. Some properties of cytochrome co, which receives its electrons from cytochrome c, are reported.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Metabolic regulation including anaerobic metabolism in Paracoccus denitrificans. 205 Jun 53

In the nitrate reductase system of Escherichia coli, the maximal expression of the nar operon is obtained under anaerobiosis in the presence of nitrate. Mudl (Ap,lac) insertion mutants, which only grew on lactose anaerobically if supplemented with nitrate were mapped at the chlC locus at min 27 of the map. In these fusion strains which lack benzyl viologen dependent nitrate reductase (NR) activity as well as the formiate-linked NR activity, the synthesis of beta-galactosidase reflects the regulation of the wild type nar operon at the transcriptional level. From these strains, two classes of spontaneous regulatory mutants were isolated: class I mutants which synthesized beta-galactosidase in anaerobiosis in the absence of nitrate and class II mutants in which the synthesis of that enzyme was partially independent of nitrate and it was no longer repressed by oxygen. The class I regulatory mutation was tightly linked to the nar operon as shown by bacteriophage P1 transductions. It probably affects either a closely linked cis-active element or a gene coding for a negative regulatory protein.
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PMID:Isolation and characterization of mutants affected in the expression of the nar operon Escherichia coli. 213 55

Two nitrate reductases, nitrate reductase A and nitrate reductase Z, exist in Escherichia coli. The nitrate reductase Z enzyme has been purified from the membrane fraction of a strain which is deleted for the operon encoding the nitrate reductase A enzyme and which harbours a multicopy plasmid carrying the nitrate reductase Z structural genes; it was purified 219 times with a yield of about 11%. It is an Mr-230,000 complex containing 13 atoms iron and 12 atoms labile sulfur/molecule. The presence of a molybdopterin cofactor in the nitrate reductase Z complex was demonstrated by reconstitution experiments of the molybdenum-cofactor-deficient NADPH-dependent nitrate reductase activity from a Neurospora crassa nit-1 mutant and by fluorescence emission and excitation spectra of stable derivatives of molybdoterin extracted from the purified enzyme. Both nitrate reductases share common properties such as relative molecular mass, subunit composition and electron donors and acceptors. Nevertheless, they diverge by two properties: their electrophoretic migrations are very different (RF of 0.38 for nitrate reductase Z versus 0.23 for nitrate reductase A), as are their susceptibilities to trypsin. An immunological study performed with a serum raised against nitrate reductase Z confirmed the existence of common epitopes in both complexes but unambiguously demonstrated the presence of specific determinants in nitrate reductase Z. Furthermore, it revealed a peculiar aspect of the regulation of both nitrate reductases: the nitrate reductase A enzyme is repressed by oxygen, strongly inducible by nitrate and positively controlled by the fnr gene product; on the contrary, the nitrate reductase Z enzyme is produced aerobically, barely induced by nitrate and repressed by the fnr gene product in anaerobiosis.
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PMID:Purification and further characterization of the second nitrate reductase of Escherichia coli K12. 213 7

Anaerobic nitrate respiration is regulated by oxygen at the level of nitrate transport; however, the mechanism of O2 inhibition is unknown. Potentially, oxygen could inhibit directly by causing conformational changes in the porter system or indirectly through diversion of electron flow from the nitrate reductase complex to oxygen reduction. Inhibition due to electron diversion implies that nitrate reduction is required for nitrate transport. In this regard, nitrate uptake and its regulation by oxygen were studied in mutants of Escherichia coli (strain AN386) deficient in cytochrome d (RG98), cytochrome o (RG101), and a mutant deficient in both cytochrome d and cytochrome o (RG99). Respiratory nitrate uptake in RG99 was highly resistant to the effects of oxygen supporting the indirect mechanism of electron diversion in oxygen regulation. Nitrate transport in RG98 and RG101 is highly sensitive to oxygen; these mutants exhibited 81 and 85% inhibition, respectively, which is similar to inhibition in the wild type. These results indicate that during nitrate respiration, O2 inhibits transport by limiting the supply of electrons to the nitrate reductase complex.
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PMID:Oxygen regulation of nitrate transport by diversion of electron flow in Escherichia coli. 217 Apr 3


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