title: Direct electrochemistry of nitrate reductase from the fungus Neurospora crassa.
abstract: We report the first direct (unmediated) catalytic electrochemistry of a eukaryotic nitrate reductase (NR). NR from the filamentous fungus Neurospora crassa, is a member of the mononuclear molybdenum enzyme family and contains a Mo, heme and FAD cofactor which are involved in electron transfer from NAD(P)H to the (Mo) active site where reduction of nitrate to nitrite takes place. NR was adsorbed on an edge plane pyrolytic graphite (EPG) working electrode. Non-turnover redox responses were observed in the absence of nitrate from holo NR and three variants lacking the FAD, heme or Mo cofactor. The FAD response is due to dissociated cofactor in all cases. In the presence of nitrate, NR shows a pronounced cathodic catalytic wave with an apparent Michaelis constant (KM) of 39μM (pH7). The catalytic cathodic current increases with temperature from 5 to 35°C and an activation enthalpy of 26kJmol(-1) was determined. In spite of dissociation of the FAD cofactor, catalytically activity is maintained.
authors.affiliation: School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane 4072, Australia.
authors.forename: Palraj
authors.initials: P
authors.lastname: Kalimuthu
authors.affiliation: Department of Plant Biology, Braunschweig University of Technology, 38106 Braunschweig, Germany.
authors.forename: Phillip
authors.initials: P
authors.lastname: Ringel
authors.affiliation: Department of Plant Biology, Braunschweig University of Technology, 38106 Braunschweig, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Kruse
authors.affiliation: School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane 4072, Australia. Electronic address: p.bernhardt@uq.edu.au.
authors.forename: Paul V
authors.initials: PV
authors.lastname: Bernhardt
mesh_terms: D002384:Catalysis; D004563:Electrochemistry; D006863:Hydrogen-Ion Concentration; D009492:Neurospora crassa / Q000201:enzymology*; D050901:Nitrate Reductase / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000494:pharmacology; D013696:Temperature
chemical_list: D050901:Nitrate Reductase; D010100:Oxygen
keywords: Enzyme; Molybdenum; Nitrate reductase; Voltammetry