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)

narK mutants of Escherichia coli produce wild-type levels of nitrate reductase but, unlike the wild-type strain, do not accumulate nitrite when grown anaerobically on a glucose-nitrate medium. Comparison of the rates of nitrate and nitrite metabolism in cultures growing anaerobically on glucose-nitrate medium revealed that a narK mutant reduced nitrate at a rate only slightly slower than that in the NarK+ parental strain. Although the specific activities of nitrate reductase and nitrite reductase were similar in the two strains, the parental strain accumulated nitrite in the medium in almost stoichiometric amounts before it was further reduced, while the narK mutant did not accumulate nitrite in the medium but apparently reduced it as rapidly as it was formed. Under conditions in which nitrite reductase was not produced, the narK mutant excreted the nitrite formed from nitrate into the medium; however, the rate of reduction of nitrate to nitrite was significantly slower than that of the parental strain or that which occurred when nitrite reductase was present. These results demonstrate that E. coli is capable of taking up nitrate and excreting nitrite in the absence of a functional NarK protein; however, in growing cells, a functional NarK promotes a more rapid rate of anaerobic nitrate reduction and the continuous excretion of the nitrite formed. Based on the kinetics of nitrate reduction and of nitrite reduction and excretion in growing cultures and in washed cell suspensions, it is proposed that the narK gene encodes a nitrate/nitrite antiporter which facilitates anaerobic nitrate respiration by coupling the excretion of nitrite to nitrate uptake. The failure of nitrate to suppress the reduction of trimethylamine N-oxide in narK mutants was not due to a change in the level of trimethylamine N-oxide reductase but apparently resulted from a relative decrease in the rate of anaerobic nitrate reduction caused by the loss of the antiporter system.
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PMID:NarK enhances nitrate uptake and nitrite excretion in Escherichia coli. 204 60

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

Nitrate transport and its regulation by oxygen was studied in denitrifying halophilic Pseudomonas stutzeri, strain Zobell, and a Tn-5 transposon nitrite reductase mutant of this organism. The rate of nitrate transport was found to be 130 nanomoles nitrate min-1 mg protein-1 and 150 nanomoles nitrate min-1 mg protein-1 in the wildtype and the nitrite reductase mutant respectively as compared to 26.4 nanomoles nitrate min-1 mg protein-1 in a non-halophilic Pseudomonas stutzeri. Asparagine was found to be the best energy source for nitrate uptake. The ratio of nitrate import to nitrite export was established by measuring extracellular nitrate and nitrite concentrations using HPLC/UV analysis. There was a 1.3:1 (NO3-/NO2-) exchange. High concentrations of nitrate during growth was found to have a negative effect on nitrite metabolism. Oxygen exerted an inhibitory effect on nitrate uptake which was reversible and more pronounced in cells grown on low concentrations of nitrate compared to cells grown at high concentrations of nitrate.
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PMID:Regulation and energization of nitrate transport in a halophilic Pseudomonas stutzeri. 215 8

Operon fusion strains and mutants of Escherichia coli K-12 lacking the NADH-dependent nitrite reductase have been used to determine the regulation and physiological roles of two independent pathways for nitrite reduction to ammonia. Both the formate- and NADH-dependent pathways (Nrf and Nir, respectively) were totally repressed during aerobic growth, partially active during anaerobic growth in the absence of nitrite and further induced anaerobically by nitrite. Both were dependent upon a functional Fnr protein (a transcription activator of genes for anaerobic respiration). During anaerobic growth in the presence of nitrate, the Nir pathway was fully induced but Nrf was strongly repressed. Mutants defective in the NarL protein, which induces transcription of nitrate reductase genes but represses fumarate reductase genes in the presence of nitrate, were derepressed for Nrf activity during growth with nitrate, but the Nir enzyme was less active. The synthesis of Nrf components was also sensitive to glucose repression and weak activation by NarL during growth in the absence of nitrate. These data indicate that the Nir pathway provides a mechanism for detoxifying nitrite formed in the cytoplasm as a product of nitrate reduction. In contrast, the electrogenic reduction of nitrite by the Nrf pathway provides a secondary source of energy during anaerobic growth and is consequently repressed by the NarL protein when the thermodynamically more favourable electron acceptor, nitrate, is available. Two short DNA sequences, 5'-TACCAT-3' and 5'-CTCCTT-3', were found in the promoters of operons known to be activated or repressed by the NarL protein.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Different physiological roles of two independent pathways for nitrite reduction to ammonia by enteric bacteria. 217 95

Nitrate and nitrite was reduced by Escherichia coli E4 in a L-lactate (5 mM) limited culture in a chemostat operated at dissolved oxygen concentrations corresponding to 90-100% air saturation. Nitrate reductase and nitrite reductase activity was regulated by the growth rate, and oxygen and nitrate concentrations. At a low growth rate (0.11 h-1) nitrate and nitrite reductase activities of 200 nmol.mg-1 protein.min-1 and 250 nmol.mg-1 protein.min-1 were measured, respectively. At a high growth rate (0.55 h-1) both enzyme activities were considerably lower (25 and 12 nmol mg-1.protein.min-1). The steady state nitrite concentration in the chemostat was controlled by the combined action of the nitrate and nitrite reductase. Both nitrate and nitrite reductase activity were inversely proportional to the growth rate. The nitrite reductase activity decreased faster with growth rate than the nitrate reductase. The chemostat biomass concentration of E. coli E4, with ammonium either solely or combined with nitrate as a source of nitrogen, remained constant throughout all growth rates and was not affected by nitrite concentrations. Contrary to batch, E. coli E4 was able to grow in continuous cultures on nitrate as the sole source of nitrogen. When cultivated with nitrate as the sole source of nitrogen the chemostat biomass concentration is related to the activity of nitrate and nitrite reductase and hence, inversely proportional to growth rate.
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PMID:Aerobic nitrate and nitrite reduction in continuous cultures of Escherichia coli E4. 219 29

We cloned the narL gene, required for nitrate induction of respiratory nitrate reductase synthesis, from Klebsiella pneumoniae. The E. coli narL gene product shares sequence similarity with the response regulator proteins of two-component regulatory systems. We found that narL(+)-containing plasmids restored nitrate regulation of anaerobic respiratory gene expression in appropriate Escherichia coli hosts. The K. pneumoniae narL region encoded a protein whose migration in Laemmli gels was indistinguishable from that of the narL product of E. coli. We constructed a narL::Km mutant of K. pneumoniae. This mutation abolished nitrate induction of respiratory nitrate reductase synthesis but had no effect on nitrate induction of assimilatory nitrate and nitrite reductase synthesis. We conclude that K. pneumoniae has distinct nitrate-responsive regulators for controlling respiratory and assimilatory gene expression.
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PMID:Genetic evidence that NarL function is not required for nitrate regulation of nitrate assimilation in Klebsiella pneumoniae M5al. 219 61

Genomic clones containing the entire crnA-niiA-niaD gene cluster of Aspergillus nidulans have been isolated, and the structures of the niiA and niaD genes have been determined by nucleotide sequence analysis. This gene cluster is required for the assimilation of nitrate in A. nidulans, and the three genes encode a product required for nitrate uptake and the enzymes, nitrite reductase and nitrate reductase, respectively. The putative coding sequences, as deduced by comparison to cDNA clones of both niiA and niaD, are interrupted by multiple small introns, and the two genes are divergently transcribed. Identification and characterization of specific mRNAs involved in nitrate assimilation indicates that only monocistronic transcripts are involved, and that the approximate sizes of these transcripts are 1.6 kb, 3.4 kb and 2.8 kb for crnA, niiA and niaD, respectively. The results also indicate that control of niiA and niaD gene expression is mediated by the levels of mRNA accumulation, in response to the source of nitrogen in the growth medium. Two types of transcripts for niiA were observed.
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PMID:Isolation and characterisation of the crnA-niiA-niaD gene cluster for nitrate assimilation in Aspergillus nidulans. 220 30

Klebsiella aerogenes W70 could grow aerobically with nitrate or nitrite as the sole nitrogen source. The assimilatory nitrate reductase and nitrite reductase responsible for this ability required the presence of either nitrate or nitrite as an inducer, and both enzymes were repressed by ammonia. The repression by ammonia, which required the NTR (nitrogen regulatory) system (A. Macaluso, E. A. Best, and R. A. Bender, J. Bacteriol. 172:7249-7255, 1990), did not act solely at the level of inducer exclusion, since strains in which the expression of assimilatory nitrate reductase and nitrite reductase was was independent of the inducer were also susceptible to repression by ammonia. Insertion mutations in two distinct genes, neither of which affected the NTR system, resulted in the loss of both assimilatory nitrate reductase and nitrite reductase. One of these mutants reverted to the wild type, but the other yielded pseudorevertants at high frequency that were independent of inducer but still responded to ammonia repression.
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PMID:Regulation of assimilatory nitrate reductase formation in Klebsiella aerogenes W70. 225 83

Three species of denitrifying bacteria, Paracoccus denitrificans, Pseudomonas stutzeri strain JM300, and Achromobacter cycloclastes, were allowed to reduce nitrate or nitrite in anaerobic, closed vials while the equilibration of gases between aqueous and gas phases was facilitated by vigorous stirring. The gas phase was sampled and analyzed for NO with use of a chemiluminescence detector calibrated against bottled NO standards or against NO produced by the nitrite-iodide reaction. [NOaq] was inferred from [NOg] and the solubility of NO. NO was detected only during denitrification in amounts that, once established, did not change with time, were independent of the initial concentration of nitrate or nitrite, and were largely independent of cell concentration, at least when nitrate was the oxidant. The usual level of NO was promptly re-established following the addition of exogenous NO or following the loss of NO by sparging. The aforementioned properties are expected for a steady-state intermediate in denitrification. Steady-state [NOaq] ranged between 1 and 65 nM depending on species and conditions. Similar results were also obtained in a related experiment in which P. stutzeri strain ZoBell respired nitrite under growth conditions. The very low steady-state [NOaq] observed during denitrification imply that the maximum activity of nitric oxide reductase in vivo, if it could be realized, would be large relative to that for nitrite reductase. This circumstance allows NO to be an intermediate without reaching toxic steady-state levels.
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PMID:Steady-state nitric oxide concentrations during denitrification. 236 85

Various heterotrophic nitrifiers have been tested and found to also be aerobic denitrifiers. The simultaneous use of two electron acceptors (oxygen and nitrate) permits these organisms to grow more rapidly than on either single electron acceptor, but generally results in a lower yield than is obtained on oxygen, alone. One strain, formerly known as "Pseudomonas denitrificans", was grown in the chemostat and shown to achieve nitrification rates of up to 44 nmol NH3 min-1 mg protein-1 and denitrification rates up to 69 nmol NO3(-1) min-1 mg protein-1. Unlike Thiosphaera pantotropha, this strain needed to induce its nitrate reductase. However, the remainder of the denitrifying pathway was constitutive and, like T. pantotropha, "Ps. denitrificans" probably possesses the copper nitrite reductase.
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PMID:Aerobic denitrification in various heterotrophic nitrifiers. 261 86


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