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 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.

Involvement of nitric oxide in the inhibition of nitrogenase activity by nitrate in Lotus root nodules, nitrate reductase. Schulzke C. Representative redox isomers are shown in Fig.

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.

Denitrification is a type of anaerobic respiration that uses nitrate as an electron acceptor. In anaerobic respiration, denitrification utilizes nitrate NO 3 — as a terminal electron acceptor in the respiratory electron transport chain. Denitrification is a widely used process; many facultative anaerobes use denitrification because nitrate, like oxygen, has a high reduction potential. Denitrification is a microbially facilitated process involving the stepwise reduction of nitrate to nitrite NO 2 — nitric oxide NO , nitrous oxide N 2 O , and, eventually, to dinitrogen N 2 by the enzymes nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase. Protons are transported across the membrane by the initial NADH reductase, quinones and nitrous oxide reductase to produce the electrochemical gradient critical for respiration. Some organisms e. Others e. Paracoccus denitrificans or Pseudomonas stutzeri reduce nitrate completely. Complete denitrification is an environmentally significant process because some intermediates of denitrification nitric oxide and nitrous oxide are significant greenhouse gases that react with sunlight and ozone to produce nitric acid, a component of acid rain.

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. A few algal strains contain NO synthase NOS , which appears to be absent in all other algae and land plants. The experimental data have led to the hypothesis that molybdoenzyme nitrate reductase NR is the main enzyme responsible for NO production in most plants. PII protein, which senses and integrates the signals of the C—N balance in the cell, likely has an important role in organizing cell responses. Here, we critically analyze these topics. Nitric oxide NO is a gaseous secondary messenger in humans, animals, plants, fungi, and bacteria. In plants, NO is involved in important physiological processes, such as growth, development, metabolism, leaf senescence, biotic and abiotic stress, defense processes, and plant—pathogen interactions, which have been extensively reviewed [ 1 , 2 , 3 , 4 , 5 ].

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Thus, photosynthesis is required for NR activation. Since the first report of Nap several functionally diverse Nap enzymes have been isolated from a variety of prokaryotes see Section 3. Each spectrum series is drawn from a representative experiment of eight A and five B biological replicates. Sign In or Create an Account. Glutamine synthetase in Medicago truncatula, unveiling new secrets of a very old enzyme. Drug Discovery. This would be expected for molybdopterin proteins that share a high degree of sequence similarity, and the extra residues are distributed over themolecular surface. The latter, evolved from experimental device described previously Roby et al. Zweier, J. Annual Review of Cell Biology 10 , 55 — Chemical Reviews. Future studies should elaborate this aspect more. In a recent study dealing with the role of M. Nature Reviews. Aging in legume symbiosis.

Nitrate NO 3 is a nitrogen-containing molecule that can be reduced by some bacterial species, but not others. Therefore, examining the ability of bacterial species to conduct nitrogen reduction is useful for characterizing and identifying bacterial species. Reduction of nitrate generally occurs during anaerobic respiration in which an organism derives its oxygen from nitrate to serve as the final electron acceptor to remove electrons from the electron transport chain.

Johansson Department of Physiology and Pharmacology, Karolinska Institutet for kindly providing us with the human liver samples and J. One very simple but important prerequisite for observing this rapid modulation was to measure NR activity in the presence of millimolar concentrations of divalent cations instead of using phosphate buffers which had been frequently applied. Early intravenous infusion of sodium nitrite protects brain against in vivo ischemia-reperfusion injury. Besson-Bard, A. Gut 35 , — During the infection phase, at 10 hpi, the increase in Mt NR1 and Mt NR2 expression is accompanied by a slight increase in NR activity, while the production of NO increases by a factor of 2, suggesting that NRs are probably not the only sources of NO. Gates et al. Its function is not clear. In this respect the nitrate anion remains an enigmatic species that promises to offer exciting science in years to come. Rowland Lewis J. Kaiser , Werner M. Sargent F.