Nitrate reductase

Nitrate reductase NR is the first enzyme of the nitrogen reduction pathway in plants, leading to the production of ammonia. However, nitrate reductase, in the nitrogen-fixing symbiosis between legumes and rhizobia, atmospheric nitrogen N 2 is directly reduced to ammonia by the nitrate reductase nitrogenase, which questions the role of NR in symbiosis.

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.

Nitrate reductase

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. Similar effects of nitrate were seen in endothelial NO synthase—deficient and germ-free mice, thereby excluding vascular NO synthase activation and bacteria as the source of nitrite. Nitrate pretreatment attenuated the increase in systemic blood pressure caused by NO synthase inhibition and enhanced blood flow during post-ischemic reperfusion. Our findings suggest a role for mammalian nitrate reduction in regulation of nitrite and NO homeostasis. This is a preview of subscription content, access via your institution. Forstermann, U.

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Federal government websites often end in. The site is secure. The nitrate anion is a simple, abundant and relatively stable species, yet plays a significant role in global cycling of nitrogen, global climate change, and human health. Although it has been known for quite some time that nitrate is an important species environmentally, recent studies have identified potential medical applications. In this respect the nitrate anion remains an enigmatic species that promises to offer exciting science in years to come.

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.

Nitrate reductase

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. In some species, nitrate is reduced to nitrite leaving nitrite as evidence of the process:. In still other bacterial species, denitrification occurs where nitrate is reduced completely to N 2 gas and becomes largely unavailable to most living things as a nitrogen source:. Nitrate broth is used to determine if an organism can reduce nitrate. Some bacteria can reduce nitrate NO 3 to nitrite NO 2 by producing the enzyme nitrate reductase.

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Miranda, K. Each spectrum series is drawn from a representative experiment of eight A and five B biological replicates. The presence of these genes varies among organisms and no solitary nap gene can be considered ubiquitous to all napA encoding organisms. In Bradyrhizobium japonicum napEDABC expression is also up-regulated in response to micro-aerophillic growth and the presence of nitrate. Thus, the molecular background and the physiological relevance of these deviating properties of Ricinus NR are still obscure. Whether the differences in the amino acid content and size affect protein function needs to be explored. Article Google Scholar. NO is a reactive free radical gaseous molecule with a broad spectrum of regulatory functions in plant growth and development, and in response to abiotic and biotic factors Kolbert et al. This review has two major sections: in the first section, nitrate in the nitrogen cycle and human health, taxonomy of nitrate reductases, assimilatory and dissimilatory nitrate reduction, cellular locations of nitrate reductases, structural and redox chemistry are discussed. Blood , — In general, volatile nitrogen compounds e.

The periplasmic nitrate reductase NapAB from Cupriavidus necator is a heterodimeric protein that belongs to the dimethyl sulfoxide reductase family of mononuclear Mo-containing enzymes and catalyzes the reduction of nitrate to nitrite. The protein comprises a large catalytic subunit NapA, 91 kDa containing the molybdenum active site plus one [4Fe-4S] cluster, as well as a small subunit NapB, 17 kDa , which is a diheme c-type cytochrome involved in electron transfer.

The acetylene-ethylene assay for N 2 fixation: laboratory and field evaluation. Roby, C. Concentration dependent regulation is indicated with brackets surrounding the chemical, for example [O 2 ]. Constructs were checked by sequencing, introduced by electroporation into Agrobacterium rhizogenes strain ARqua1, and used for M. Surprisingly, in anoxic leaf tissues, the reduction of nitrate and the accumulation of nitrite are still much lower than should be expected from the high NR activity determined in the extracts. Nitrate entry and nitrite formation in the infected region of soybean nodules. Yersinia pestis 5 strains , enterocolitica. PMC If so, the impact of their redox state on function remains to be established. Authoring Open access Purchasing Institutional account management Rights and permissions. MacKintosh C. Medicago truncatula cv Jemalong A17 were scarified, sterilized, and germinated as in del Giudice et al. It was concluded that assimilate translocation from shoot to root will also affect the nitrate reduction rate of roots, but this is probably a slow response.