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)

There was a long-held belief that the gram-positive soil bacterium Bacillus subtilis is a strict aerobe. But recent studies have shown that B. subtilis will grow anaerobically, either by using nitrate or nitrite as a terminal electron acceptor, or by fermentation. How B. subtilis alters its metabolic activity according to the availability of oxygen and alternative electron acceptors is but one focus of study. A two-component signal transduction system composed of a sensor kinase, ResE, and a response regulator, ResD, occupies an early stage in the regulatory pathway governing anaerobic respiration. One of the essential roles of ResD and ResE in anaerobic gene regulation is induction of fnr transcription upon oxygen limitation. FNR is a transcriptional activator for anaerobically induced genes, including those for respiratory nitrate reductase, narGHJI.B. subtilis has two distinct nitrate reductases, one for the assimilation of nitrate nitrogen and the other for nitrate respiration. In contrast, one nitrite reductase functions both in nitrite nitrogen assimilation and nitrite respiration. Unlike many anaerobes, which use pyruvate formate lyase, B. subtilis can carry out fermentation in the absence of external electron acceptors wherein pyruvate dehydrogenase is utilized to metabolize pyruvate.
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PMID:Anaerobic growth of a "strict aerobe" (Bacillus subtilis). 989 97

This review presents some aspects of a concept of cellular evolution bearing a relationship to nitrate--nitrite respiration, the endosymbiosis theory, and the origin of NO synthase and nitrite reductase activity in heme-containing proteins. Analysis of structural and functional unity of the NO synthase and nitrite reductase systems suggests that these systems did not arise without any relation to evolutionarily ancient energetic systems of cells. The use of symmetry principles reveals commonalities among many electron transport chains which in the language of physics is called "invariance". This work also comparatively analyzes the nitric oxide cycle and the known nitrogen cycle. The ideas about evolution of the NO synthase and nitrite reductase systems developed here are clearly compatible with the endosymbiotic theory and the hypothesis that nitrate--nitrite respiration was a precursor of oxygen-dependent respiration.
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PMID:Biochemical predetermination of the NO synthase and nitrite reductase components of the nitric oxide cycle. 1038 13

The enzyme cytochrome c nitrite reductase catalyses the six-electron reduction of nitrite to ammonia as one of the key steps in the biological nitrogen cycle, where it participates in the anaerobic energy metabolism of dissimilatory nitrate ammonification. Here we report on the crystal structure of this enzyme from the microorganism Sulfurospirillum deleyianum, which we solved by multiwavelength anomalous dispersion methods. We propose a reaction scheme for the transformation of nitrite based on structural and spectroscopic information. Cytochrome c nitrite reductase is a functional dimer, with 10 close-packed haem groups of type c and an unusual lysine-coordinated high-spin haem at the active site. By comparing the haem arrangement of this nitrite reductase with that of other multihaem cytochromes, we have been able to identify a family of proteins in which the orientation of haem groups is conserved whereas structure and function are not.
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PMID:Structure of cytochrome c nitrite reductase. 1044 Mar 80

This study provides preliminary evidence that NO production could be a general attribute of algae. Anabaena doliolum was found to be a better NO producer than Scenedesmus and Synechoccocus. Experiments conducted with inhibitors of photosynthesis (DCMU), ATP synthesis (DCCD), and the uncoupler (2,4-DNP) and its analog arsenate clearly revealed that inhibition of nitrite assimilation through the blockage of nitrite reductase (NiR) is primarily responsible for NO emission. A linear relationship between nitrite concentration in the culture medium and NO in the exhaust gas supports the view that accumulation of nitrite is responsible for NO formation. A failure of Scenedesmus, grown in the medium substituted with W for Mo, to produce either NO/NO-2 in light or a 'light-off' peak, and a resumption of these activities upon the addition of Mo proved beyond doubt that a functional nitrate reductase (NR) is necessary for the production of nitrite and NO by algae grown on nitrate as the nitrogen source. Moreover, the appearance of a NO peak immediately after nitrite supplementation under dark conditions in W-substituted cultures with or without glucose ruled out an enzymatic role of NR in NO emission.
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PMID:Studies on nitric oxide (NO) formation by the green alga Scenedesmus obliquus and the diazotrophic cyanobacterium Anabaena doliolum. 1052 Apr 83

This work evaluates the impact that the application of different mulches exerts on nitrogen (N) metabolism in roots and leaves and on yield of potato tubers (Solanum tuberosum var. Spunta). The parameters analyzed in this experiment were root temperature; nitrate reductase and nitrite reductase activities; concentrations of nitrates, ammonium, amino acids, proteins, and organic N; dry weight of roots and leaves; and tuber yield. Use of white polyethylene (T2) and white-black plastic (T3) promoted optimal root temperatures for plant growth (23-27 degrees C). Under these experimental conditions, plants showed the greatest efficiency in N utilization and the greatest yield in tubers. Considering the sensitivity of this plant to thermal stress, high root temperatures caused by black polyethylene (>31 degrees C) (T4) depressed N metabolism as well as yield, compared with the results of T2 and T3. Finally, clear polyethylene plastic (T1) caused more damage than did the absence of mulch (control, T0).
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PMID:Potato performance in response to different mulches. 1. Nitrogen metabolism and yield. 1055 41

The nrtP and narB genes, encoding nitrate/nitrite permease and nitrate reductase, respectively, were isolated from the marine cyanobacterium Synechococcus sp. strain PCC 7002 and characterized. NrtP is a member of the major facilitator superfamily and is unrelated to the ATP-binding cassette-type nitrate transporters that previously have been described for freshwater strains of cyanobacteria. However, NrtP is similar to the NRT2-type nitrate transporters found in diverse organisms. An nrtP mutant strain consumes nitrate at a 4.5-fold-lower rate than the wild type, and this mutant grew exponentially on a medium containing 12 mM nitrate at a rate approximately 2-fold lower than that of the wild type. The nrtP mutant cells could not consume nitrite as rapidly as the wild type at pH 10, suggesting that NrtP also functions in nitrite uptake. A narB mutant was unable to grow on a medium containing nitrate as a nitrogen source, although this mutant could grow on media containing urea or nitrite with rates similar to those of the wild type. Exogenously added nitrite enhanced the in vivo activity of nitrite reductase in the narB mutant; this suggests that nitrite acts as a positive effector of nitrite reductase. Transcripts of the nrtP and narB genes were detected in cells grown on nitrate but were not detected in cells grown on urea or ammonia. Transcription of the nrtP and narB genes is probably controlled by the NtcA transcription factor for global nitrogen control. The discovery of a nitrate/nitrite permease in Synechococcus sp. strain PCC 7002 suggests that significant differences in nutrient transporters may occur in marine and freshwater cyanobacteria.
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PMID:A novel nitrate/nitrite permease in the marine Cyanobacterium synechococcus sp. strain PCC 7002. 1057 42

We constructed mutant strains lacking the nitrite reductase (NR) gene in Chlamydomonas reinhardtii. Two types of NR mutants were obtained, which either have or lack the high-affinity nitrate transporter (Nrt2;1, Nrt2;2, and Nar2) genes. None of these mutants overexpressed nitrate assimilation gene transcripts nor NR activity in nitrogen-free medium, in contrast to NR mutants. This finding confirms the previous role proposed for NR on its own regulation (autoregulation) and on the other genes for nitrate assimilation in C. reinhardtii. In addition, the NR mutants were used to study nitrate transporters from nitrite excretion. At high CO(2), only strains carrying the above high-affinity nitrate transporter genes excreted stoichiometric amounts of nitrite from 100 microM nitrate in the medium. A double mutant, deficient in both the high-affinity nitrate transporter genes and NR, excreted nitrite at high CO(2) only when nitrate was present at mM concentrations. This suggests that there exists a low-affinity nitrate transporter that might correspond to the nitrate/nitrite transport system III. Moreover, under low CO(2) conditions, the double mutant excreted nitrite from nitrate at micromolar concentrations by a transporter with the properties of the nitrate/nitrite transport system IV.
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PMID:Nitrite reductase mutants as an approach to understanding nitrate assimilation in Chlamydomonas reinhardtii. 1063 Dec 72

In the cyanobacterium Synechococcus sp. strain PCC 7942, the phosphorylation states of the signal transducer PII protein (GlnB) can change rapidly depending on the nitrogen and carbon supply. A PII-null mutant (MP2) shows no ammonium-dependent inhibition of the nitrate and nitrite uptake, in contrast to the wild-type. New mutants with different types of PII, which may mimic either the phosphorylated (GlnBS49E or GlnBS49D) or unphosphorylated (GlnBS49A) form of the protein, were constructed using site-directed in vitro mutagenesis. Mutant MP2-A (GlnBS49A) grew poorly using nitrate as a nitrogen source and was unable to take up nitrate supplied at 100 microM, even in the absence of externally added ammonium. Mutants MP2-D and MP2-E (GlnBS49D and GlnBS49E, respectively), however, showed nitrate-dependent growth and regulation of nitrate uptake by ammonium, as in the wild-type. Characterization of the mutants also included an analysis of nitrite uptake and of the levels of the nir (nitrate/nitrite assimilation) operon transcripts, the presence of NrtA (nitrate/nitrite transport binding protein), and nitrate and nitrite reductase activities. In vitro, no significant difference was observed in the cooperative binding of ATP and 2-oxoglutarate between the wild-type and the unphosphorylated or phosphorylated-like forms of the mutant PII proteins. The results obtained indicate that both unphosphorylated and phosphorylated-like forms of PII are able to inhibit nitrate uptake in the presence of ammonium, but the unphosphorylated form also has a negative effect in the absence of this nitrogen source. Therefore, an additional effector, possibly 2-oxoglutarate, is required for the PII protein to relieve inhibition of nitrate uptake in the absence of ammonium.
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PMID:Phosphorylation of the signal transducer PII protein and an additional effector are required for the PII-mediated regulation of nitrate and nitrite uptake in the Cyanobacterium synechococcus sp. PCC 7942. 1063 30

The genome sequence of the extremely thermophilic bacterium Aquifex aeolicus encodes alternative sigma factor sigma(N) (sigma(54), RpoN) and five potential sigma(N)-dependent transcriptional activators. Although A. aeolicus possesses no recognizable nitrogenase genes, two of the activators have a high degree of sequence similarity to NifA proteins from nitrogen-fixing proteobacteria. We identified five putative sigma(N)-dependent promoters upstream of operons implicated in functions including sulfur respiration, nitrogen assimilation, nitrate reductase, and nitrite reductase activity. We cloned, overexpressed (in Escherichia coli), and purified A. aeolicus sigma(N) and the NifA homologue, AQ_218. Purified A. aeolicus sigma(N) bound to E. coli core RNA polymerase and bound specifically to a DNA fragment containing E. coli promoter glnHp2 and to several A. aeolicus DNA fragments containing putative sigma(N)-dependent promoters. When combined with E. coli core RNA polymerase, A. aeolicus sigma(N) supported A. aeolicus NifA-dependent transcription from the glnHp2 promoter. The E. coli activator PspFDeltaHTH did not stimulate transcription. The NifA homologue, AQ_218, bound specifically to a DNA sequence centered about 100 bp upstream of the A. aeolicus glnBA operon and so is likely to be involved in the regulation of nitrogen assimilation in this organism. These results argue that the sigma(N) enhancer-dependent transcription system operates in at least one extreme environment, and that the activator and sigma(N) have coevolved.
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PMID:Functionality of purified sigma(N) (sigma(54)) and a NifA-like protein from the hyperthermophile Aquifex aeolicus. 1069 67

Cytochrome c nitrite reductase catalyzes the six-electron reduction of nitrite to ammonia as a key step within the biological nitrogen cycle. Most recently, the crystal structure of the soluble enzyme from Sulfurospirillum deleyianum could be solved to 1.9 A resolution. This set the basis for new experiments on structural and functional aspects of the pentaheme protein which carries a Ca(2+) ion close to the active site heme. In the crystal, the protein was a homodimer with ten hemes in very close packing. The strong interaction between the nitrite reductase monomers also occurred in solution according to the dependence of the activity on the protein concentration. Addition of Ca(2+) to the enzyme as isolated had a stimulating effect on the activity. Ca(2+) could be removed from the enzyme by treatment with chelating agents such as EGTA or EDTA which led to a decrease in activity. In addition to nitrite, the enzyme converted NO, hydroxylamine and O-methyl hydroxylamine to ammonia at considerable rates. With N2O the activity was much lower; most likely dinitrogen was the product in this case. Cytochrome c nitrite reductase exhibited a remarkably high sulfite reductase activity, with hydrogen sulfide as the product. A paramagnetic Fe(II)-NO, S = 1/2 adduct was identified by rapid freeze EPR spectroscopy under turnover conditions with nitrite. This potential reaction intermediate of the reduction of nitrite to ammonia was also observed with PAPA NONOate and Spermine NONOate.
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PMID:Bacterial cytochrome c nitrite reductase: new structural and functional aspects. 1083 Aug 92


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