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)

Bacterial denitrification transforms nitrate to dinitrogen. The process is expressed facultatively in response to environmental conditions. Around 50 components make up the denitrification apparatus and its assembly pathways. We are beginning to understand how exogenous signals provided by oxygen and N oxides are processed for activating the underlying gene programs. Key signals are provided by nitrate, nitric oxide, and a low oxygen tension. In the genus Pseudomonas the nitrate signal is processed by a two component regulatory system which activates the nar operon encoding respiratory nitrate reductase. Nitric oxide is not only an essential respiratory substrate of the denitrifying cell but constitutes in nanomolar concentrations also a key signal for the expression of nitrite reductase and NO reductase which control cellular NO homeostasis. The signal pathway in the genera Pseudomonas, Paracoccus and Rhodobacter involves regulators of the FNR family of transcription factors, which cluster phylogenetically in a separate subgroup. In contrast, Ralstonia eutropha requires a sigma-54 dependent regulator of the NtrC family for the expression of its quinol-dependent NO reductase. Important questions are directed currently at the mechanism(s) of activation of these transcription factors by NO, and avoidance of crosstalk with FNR factors at target promoters operating with identical recognition motifs.
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PMID:Nitric oxide signaling and NO dependent transcriptional control in bacterial denitrification by members of the FNR-CRP regulator family. 1193 59

Neisseria meningitidis, the causative agent of meningococcal disease in humans, is likely to be exposed to nitrosative stress during natural colonization and disease. The genome of N. meningitidis includes the genes aniA and norB, predicted to encode nitrite reductase and nitric oxide (NO) reductase, respectively. These gene products should allow the bacterium to denitrify nitrite to nitrous oxide. We show that N. meningitidis can support growth microaerobically by the denitrification of nitrite via NO and that norB is required for anaerobic growth with nitrite. NorB and, to a lesser extent, the cycP gene product cytochrome c' are able to counteract toxicity due to exogenously added NO. Expression of these genes by N. meningitidis during colonization and disease may confer protection against exogenous or endogenous nitrosative stress.
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PMID:Nitric oxide metabolism in Neisseria meningitidis. 1200 39

Rhodobacter sphaeroides strain 2.4.3 is capable of diverse metabolic lifestyles, including denitrification. The regulation of many Rhodobacter genes involved in redox processes is controlled, in part, by the PrrBA two-component sensor-regulator system, where PrrB serves as the sensor kinase and PrrA is the response regulator. Four strains of 2.4.3 carrying mutations within the prrB gene were isolated in a screen for mutants unable to grow anaerobically on medium containing nitrite. Studies revealed that the expression of nirK, the structural gene encoding nitrite reductase, in these strains was significantly decreased compared to its expression in 2.4.3. Disruption of prrA also eliminated the ability to grow both photosynthetically and anaerobically in the dark on nitrite-amended medium. Complementation with prrA restored the wild-type phenotype. The PrrA strain exhibited a severe decrease in both nitrite reductase activity and expression of a nirK-lacZ fusion. Nitrite reductase activity in the PrrA strain could be restored to wild-type levels by using nirK expressed from a heterologous promoter, suggesting that the loss of nitrite reductase activity in the PrrA and PrrB mutants was not due to problems with enzyme assembly or the supply of reductant. Inactivation of prrA had no effect on the expression of the gene encoding NnrR, a transcriptional activator required for the expression of nirK. Inactivation of ccoN, part of the cbb(3)-type cytochrome oxidase shown to regulate the kinase activity of PrrB, also caused a significant decrease in both nirK expression and Nir activity. This was unexpected, since PrrA-P accumulates in the ccoN strain. Together, these results demonstrate that PrrBA plays an essential role in the regulation of nirK.
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PMID:Involvement of the PrrB/PrrA two-component system in nitrite respiration in Rhodobacter sphaeroides 2.4.3: evidence for transcriptional regulation. 1205 46

Isolated soil DNA from an oak-hornbeam forest close to Cologne, Germany, was suitable for PCR amplification of gene segments coding for the 16S rRNA and nitrogenase reductase (NifH), nitrous oxide reductase (NosZ), cytochrome cd(1)-containing nitrite reductase (NirS), and Cu-containing nitrite reductase (NirK) of denitrification. For each gene segment, diverse PCR products were characterized by cloning and sequencing. None of the 16S rRNA gene sequences was identical to any deposited in the data banks, and therefore each of them belonged to a noncharacterized bacterium. In contrast, the analyzed clones of nifH gave only a few different sequences, which occurred many times, indicating a low level of species richness in the N2-fixing bacterial population in this soil. Identical nifH sequences were also detected in PCR amplification products of DNA of a soil approximately 600 km distant from the Cologne area. Whereas biodiversity was high in the case of nosZ, only a few different sequences were obtained with nirK. With respect to nirS, cloning and sequencing of the PCR products revealed that many false gene segments had been amplified with DNA from soil but not from cultured bacteria. With the 16S rRNA gene data, many sequences of uncultured bacteria belonging to the Acidobacterium phylum and actinomycetes showed up in the PCR products when isolated DNA was used as the template, whereas sequences obtained for nifH and for the denitrification genes were closely related to those of the proteobacteria. Although in such an experimental approach one has to cope with the enormous biodiversity in soils and only a few PCR products can be selected at random, the data suggest that denitrification and N2 fixation are not genetic traits of most of the uncultured bacteria.
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PMID:Biodiversity of denitrifying and dinitrogen-fixing bacteria in an acid forest soil. 1214 77

The 1.4-A crystal structure of the oxidized state of a Y25S variant of cytochrome cd(1) nitrite reductase from Paracoccus pantotrophus is described. It shows that loss of Tyr(25), a ligand via its hydroxy group to the iron of the d(1) heme in the oxidized (as prepared) wild-type enzyme, does not result in a switch at the c heme of the unusual bishistidinyl coordination to the histidine/methionine coordination seen in other conformations of the enzyme. The Ser(25) side chain is seen in two positions in the d(1) heme pocket with relative occupancies of approximately 7:3, but in neither case is the hydroxy group bound to the iron atom; instead, a sulfate ion from the crystallization solution is bound between the Ser(25) side chain and the heme iron. Unlike the wild-type enzyme, the Y25S mutant is active as a reductase toward nitrite, oxygen, and hydroxylamine without a reductive activation step. It is concluded that Tyr(25) is not essential for catalysis of reduction of any substrate, but that the requirement for activation by reduction of the wild-type enzyme is related to a requirement to drive the dissociation of this residue from the active site. The Y25S protein retains the d(1) heme less well than the wild-type protein, suggesting that the tyrosine residue has a role in stabilizing the binding of this cofactor.
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PMID:Structure and kinetic properties of Paracoccus pantotrophus cytochrome cd1 nitrite reductase with the d1 heme active site ligand tyrosine 25 replaced by serine. 1255 30

Cytochrome c ' (cyt c ') is found in the periplasmic space of denitrifying bacteria where it is thought to mediate the transfer of NO between the nitrogen-cycle enzymes dissimilatory nitrite reductase and nitric oxide reductase. It contains a 5-coordinate (5c) His-ligated haem that shares spectroscopic and ligand-binding properties with the haem group in the sensory domain of soluble guanylate cyclase (sGC). The latter is an extremely important enzyme involved in the control of vasodilation and blood clotting. Curiously, the enzyme is activated up to 200-fold by the binding of NO to the haem, whereas the binding of CO gives rise to only a mild stimulation of activity. Through X-ray crystallography we have studied NO and CO binding to cyt c '. CO binds to the distal face to give a 6-coordinate (6c) adduct. By contrast, NO binding gives rise to a 5c adduct through the displacement of the proximal His, to give a novel and unexpected proximal binding mode for NO. These results are also supported by a range of spectroscopies. In the absence of a crystal structure for sGC we propose that cyt c ' provides a structural model for the haem domain of this enzyme and thereby helps to explain the differential effects of NO and CO on its activity.
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PMID:A two-faced molecule offers NO explanation: the proximal binding of nitric oxide to haem. 1277 55

Shewanella oneidensis is a metal reducer that can use several terminal electron acceptors for anaerobic respiration, including fumarate, nitrate, dimethyl sulfoxide (DMSO), trimethylamine N-oxide (TMAO), nitrite, and insoluble iron and manganese oxides. Two S. oneidensis mutants, SR-558 and SR-559, with Tn5 insertions in crp, were isolated and analyzed. Both mutants were deficient in Fe(III) and Mn(IV) reduction. They were also deficient in anaerobic growth with, and reduction of, nitrate, fumarate, and DMSO. Although nitrite reductase activity was not affected by the crp mutation, the mutants failed to grow with nitrite as a terminal electron acceptor. This growth deficiency may be due to the observed loss of cytochromes c in the mutants. In contrast, TMAO reduction and growth were not affected by loss of cyclic AMP (cAMP) receptor protein (CRP). Fumarate and Fe(III) reductase activities were induced in rich medium by the addition of cAMP to aerobically growing wild-type S. oneidensis. These results indicate that CRP and cAMP play a role in the regulation of anaerobic respiration, in addition to their known roles in catabolite repression and carbon source utilization in other bacteria.
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PMID:Involvement of cyclic AMP (cAMP) and cAMP receptor protein in anaerobic respiration of Shewanella oneidensis. 1277 5

In Bradyrhizobium japonicum, a gene named nnrR was identified which encodes a protein with high similarity to FNR/CRP-type transcriptional regulators. Mutant strains carrying an nnrR null mutation were unable to grow anaerobically in the presence of nitrate or nitrite, and they lacked both nitrate and nitrite reductase activities. Anaerobic activation of an nnrR'-'lacZ fusion required FixLJ and FixK(2). In turn, N oxide-mediated induction of nir and nor genes encoding nitrite and nitric oxide reductase, respectively, depended on NnrR. Thus, NnrR expands the FixLJ-FixK(2) regulatory cascade by an additional control level which integrates the N oxide signal required for maximal induction of the denitrification genes.
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PMID:Bradyrhizobium japonicum NnrR, a denitrification regulator, expands the FixLJ-FixK2 regulatory cascade. 1281 94

The denitrifying fungus Cylindrocarpon tonkinense was thought to be able to denitrify only nitrite (NO2-) but not nitrate (NO3-) to form nitrous oxide (N2O). Here we found, however, that C. tonkinense can denitrify NO3- under certain conditions. Presence of ammonium (NH3+) in addition to NO3- and the use of a fermentable sugar as an electron donor were key conditions for inducing the denitrifying activity. Such induction accompanied a remarkable increase in the intracellular level of the enzyme activities related to NO3- metabolism. These activities contained assimilatory type NADPH (or NADH)-dependent NO3- reductase (aNar), dissimilatory nitrite reductase (dNir), and nitric oxide reductase (P450nor), but did not contain ubiquinol-dependent, dissimilatory NO3- reductase (dNar). The denitrification was inhibited by tungstate, an inhibitor of Nar. These results demonstrated occurrence of a novel type of denitrification in C. tonkinense, in which assimilatory type Nar is possibly involved.
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PMID:Denitrification of nitrate by the fungus Cylindrocarpon tonkinense. 1283 90

The increase of deoxyhemoglobin nitrite-reductase activity was established at streptozotocin-induced diabetes in rats. The deoxyhemoglobin nitrosilation in the streptozotocin-induced diabetic rats was shown to increase the optical density in the aromatic acid region and cause additional absorption peak at 334 nm. The two-week injection of nicotinamide causes reduction in the nitrite reductase activity of the deoxyhemoglobin and the absorption peak at 334 nm disappearance.
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PMID:[Nitrite reductase activity of deoxyhemoglobin in diabetes and its correction by nicotinamide]. 1292 26


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