Nitrate reductase

Nitrate reductase NR is the first enzyme of the nitrogen reduction pathway in plants, leading to the production of ammonia.

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. Endothelial nitric oxide synthase in vascular disease: from marvel to menace.

The code is made of the name of the species represented, nitrate reductase name allotted to the sequence on the literature evoworld.io NCBI, and the number of amino acids composing each protein. Buy or subscribe.

Werner M. Kaiser, Steven C. Assimilatory nitrate reductase NR of higher plants is a most interesting enzyme, both from its central function in plant primary metabolism and from the complex regulation of its expression and control of catalytic activity and degradation. It is also demonstrated that stress factors like nitrate deficiency and salinity have remarkably little direct influence on the NR activation state. Further, changes in NR activity measured in vitro are not always associated with changes in nitrate reduction rates in vivo , suggesting that NR can be under strong substrate limitation. However, it is not known whether the molecular form of NR in vivo affects its susceptibility to proteolytic degradation, or whether factors that affect the NR activation state also independently affect the activity or induction of the NR protease s.

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. Crystals of the oxidized form of the enzyme diffracted beyond 1. This is the highest resolution reported to date for a nitrate reductase, providing true atomic details of the protein active center, and this showed further evidence on the molybdenum coordination sphere, corroborating previous data on the related Desulfovibrio desulfuricans NapA. The molybdenum atom is bound to a total of six sulfur atoms, with no oxygen ligands or water molecules in the vicinity.

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.

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Methods Algorithms. The Plant Cell 9 , — Nitrate reductase structure, function and regulation: bridging the gap between biochemistry and physiology. It is known that the cytosol of anoxic cells is acidified from the normal pH 7. Roux, B. Schulzke C. Nitrate reduction, nitrite reduction and ammonium assimilation in barley roots in respoinse to anoxia. The role of mitochondrial ETC in NO production during the early days of the symbiotic process remains to be clarified. The nap operons categorized into four groups based on the presence or absence of a membrane quinone oxidase napC or napH. The pterin cofactor of prokaryotic NR is modified with a guanine dinucleotide Fig. The two electron oxidation of any of the isomeric forms would lead to the fully oxidized ring open structure.

Nitrate reductase NR is an intracellular enzyme commonly occurring in the cytoplasm.

Categories : Enzymes Integral membrane proteins EC 1. Rights and permissions Reprints and permissions. Plant J. While catalyzing a single reaction, nitrate reduction to nitrite, periplasmic nitrate reductase has been linked to a number of cellular functions including the maintenance of redox poise, nitrate scavenging, nitrate respiration and pathogenicity. If the bacterial denitrification pathway, including the periplasmic nitrate reductase Nap and nitrite reductase Nir , has been described as the main enzymatic source of NO, additional genes encoding putative nitrate and nitrite reductase called narB and NirN, respectively have been recently identified that could also participate indirectly in NO synthesis Ruiz et al. The latter is often found in patients with bacteremia and gastroenteritis and can be differentiated from C. As a consequence, succinate and malate contents decreased Figures 9C, D , indicating a lower supply of carbon nutrients to bacteroids, and asparagine content decreased Figure 9E as a result of the shortage of carbon substrate supply and ARA inhibition. 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 reductases from leaves of Ricinus Ricinus communis L. Schematic diagram summarizing the multiple effects of sugars and eventually sugar phosphates on NR expression, NR activity and NR degradation. Although dissimilatory NR also forms nitrite from nitrate, nitrite can be furthermetabolized into dinitrogen or ammonia as part of denitrification or dissimilatory nitrate reduction to ammonia DNRA , respectively Fig. Nitrate reductase NR is regulated at the transcriptional and translational levels induced by light, nitrate, and possibly a negative feedback mechanism. Plant Sci. Rolin, D.