Nitrate reductase

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Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Bacteria express nitrate reductases that produce nitrite, but mammals lack these specific enzymes. Here we report on nitrate reductase activity in rodent and human tissues that results in formation of nitrite and nitric oxide NO and is attenuated by the xanthine oxidoreductase inhibitor allopurinol. Nitrate administration to normoxic rats resulted in elevated levels of circulating nitrite that were again attenuated by allopurinol.

Nitrate reductase

This reaction is critical for the production of protein in most crop plants, as nitrate is the predominant source of nitrogen in fertilized soils. Eukaryotic nitrate reductases are part of the sulfite oxidase family of molybdoenzymes. Prokaryotic nitrate reductases belong to the DMSO reductase family of molybdoenzymes and have been classified into three groups, assimilatory nitrate reductases Nas , respiratory nitrate reductase Nar , and periplasmic nitrate reductases Nap. In Nap, the molybdenum is covalently attached to the protein by a cysteine side chain, and an aspartate side chain in Nar. Prokaryotic nitrate reductases have two major types, transmembrane nitrate reductases NAR and periplasmic nitrate reductases NAP. NAR allows for proton translocation across the cellular membrane and can contribute to the generation of ATP by the proton motive force. NAP cannot do so. The transmembrane respiratory nitrate reductase [6] is composed of three subunits; an 1 alpha, 1 beta and 2 gamma. It can substitute for the NRA enzyme in Escherichia coli , allowing it to use nitrate as an electron acceptor for anaerobic respiration. The nitrate reductase of higher plants, algae, and fungi is a homodimeric cytosolic protein with five conserved domains in each monomer: 1 an Mo-MPT domain that contains the single molybdopterin cofactor, 2 a dimer interface domain, 3 a cytochrome b domain, and 4 an NADH-binding domain that combines with 5 an FAD-binding domain to form the cytochrome b reductase fragment. Its function is not clear. In prokaryotic periplasmic nitrate reductase, the nitrate anion binds to Mo IV. Oxygen transfer yields an Mo VI oxo intermediate with release of nitrite. Reduction of the Mo oxide and protonolysis removes the oxo group, regenerating Mo IV. Similar to the prokaryotic nitrate reduction mechanism, in eukaryotic nitrate reductase, an oxygen in nitrate binds to Mo in the IV oxidation state, displacing a hydroxide ion.

Free Radic. The two electron oxidation of any of the isomeric forms would lead to the fully oxidized ring open structure, nitrate reductase.

Nitrate reductase NR is the first enzyme of the nitrogen reduction pathway in plants, leading to the production of ammonia. However, in the nitrogen-fixing symbiosis between legumes and rhizobia, atmospheric nitrogen N 2 is directly reduced to ammonia by the bacterial nitrogenase, which questions the role of NR in symbiosis. Next to that, NR is the best-characterized source of nitric oxide NO in plants, and NO is known to be produced during the symbiosis. Moreover, NRs are involved together with the mitochondrial electron transfer chain in NO production throughout the symbiotic process and energy regeneration in N 2 -fixing nodules. Using an in vivo NMR spectrometric approach, we show that, in mature nodules, NRs participate also in the regulation of energy state, cytosolic pH, carbon and nitrogen metabolism under both normoxia and hypoxia. These data point to the importance of NR activity for the N 2 -fixing symbiosis and provide a first explanation of its role in this process. In plants, yeasts, algae, and fungi, nitrate reductase NR is a key enzyme of the nitrogen N reduction and assimilation pathway.

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Nitrate is generally considered a water pollutant and an undesirable fertilizer residue in the food chain. Research in the s indicated that, by reducing nitrate to nitrite, commensal bacteria might be involved in the pathogenesis of gastric cancers and other malignancies, as nitrite can enhance the generation of carcinogenic N -nitrosamines. More recent studies indicate that the bacterial metabolism of nitrate to nitrite and the subsequent formation of biologically active nitrogen oxides could be beneficial. Here, we will consider the evidence that nitrate-reducing commensals have a true symbiotic role in mammals and facilitate a previously unrecognized but potentially important aspect of the nitrogen cycle. This is a preview of subscription content, access via your institution.

Nitrate reductase

Federal government websites often end in. The site is secure. Nitric oxide is a gaseous secondary messenger that is critical for proper cell signaling and plant survival when exposed to stress. Nitric oxide NO synthesis in plants, under standard phototrophic oxygenic conditions, has long been a very controversial issue.

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The results of this study showed that the dramatic increase in nitrate reductase in anoxic conditions can be directly attributed to the anoxic conditions inducing the dissociation of protein from NR and the dephosphorylation of the nitrate reductase. In leaves, NR activity decreased whereas in roots in increased with increasing salinity. Nitrate itself appears to be a signal Scheible et al. In a recent study, Li et al. New Phytol. Google Scholar. ISBN The Plant Cell. But together with the activation of NR, anoxia always leads to a strong accumulation of nitrite and to nitrite excretion by the roots. At this time, the effect of nitrate-rich diets on the human microbiota has not been investigated fully. Green, D.

Nitrate reductase NR is an intracellular enzyme commonly occurring in the cytoplasm. This enzyme is the rate-limiting enzyme in nitrate assimilation, and its activity is strongly related to the bioavailability of nitrate.

In the desoxo-Mo complexes, the dominating effect of the terminal oxo group is absent, — and the dithiolene ligand effectively dictates the Mo ligand field, again resulting in an isolated d xy orbital in the ground state. Email: ude. Buy or subscribe. FEBS Lett. In that situation NR was still activated in the dark, whereas normally NR degradation e. The tenors of these mechanisms are very similar to that proposed for functioning of DMSO reductase where in essence the Mo-center shuttles between a desoxo-Mo iv andamonooxo-Mo vi centers. Formate dehydrogenase FDH was included in the analysis as an outlier. Acta Physiol. Permissions Icon Permissions. The expression of the different genes was normalized against two housekeeping genes Mtc27 Van de Velde et al.