title: Nitrite and nitrate reduction by molybdenum centers of the nitrate reductase type: computational predictions on the catalytic mechanism.
abstract: Nitrate reductases (NRs) are enzymes that catalyze reduction of nitrate to nitrite using a molybdenum cofactor. In an alternative reaction, plant NRs have also been shown to catalyze reduction of nitrite to nitric oxide, and this appears to be a major source of nitric oxide synthesis in plants, although other pathways have also been shown. Here, density functional theory (DFT) results are shown, indicating that although nitrate is thermodynamically the preferred substrate for the NR active site, both nitrite and nitrate are easily reduced to nitrite and NO, respectively. These mechanisms require a Mo(IV) state. Additionally, in the case of the nitrite, linkage isomerism is at work and controlled by the metal oxidation state, and reduction is, unlike in the nitrate case, dependent on protonation. The data may be relevant to other molybdenum enzymes with similar active sites, such as xanthine oxidase.
authors.affiliation: Department of Chemistry, Babes-Bolyai University, Cluj-Napoca, Romania. rsilaghi@chem.ubbcluj.ro
authors.forename: Radu
authors.initials: R
authors.lastname: Silaghi-Dumitrescu
authors.forename: Mihaela
authors.initials: M
authors.lastname: Mich
authors.forename: Csongor
authors.initials: C
authors.lastname: Matyas
authors.forename: Chris E
authors.initials: CE
authors.lastname: Cooper
mesh_terms: D001665:Binding Sites; D020134:Catalytic Domain; D008956:Models, Chemical; D008958:Models, Molecular; D008982:Molybdenum / Q000737:chemistry*; D009565:Nitrate Reductases / Q000737:chemistry* / Q000378:metabolism*; D009566:Nitrates / Q000737:chemistry / Q000378:metabolism; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism; D009573:Nitrites / Q000737:chemistry / Q000378:metabolism; D009584:Nitrogen / Q000737:chemistry
chemical_list: D009566:Nitrates; D009573:Nitrites; D009569:Nitric Oxide; D008982:Molybdenum; D009565:Nitrate Reductases; D009584:Nitrogen