title: Oxyl and hydroxyl radical transfer in mitochondrial amidoxime reducing component-catalyzed nitrite reduction.
abstract: A combination of electron paramagnetic resonance (EPR) spectroscopy and computational approaches has provided insight into the nature of the reaction coordinate for the one-electron reduction of nitrite by the mitochondrial amidoxime reducing component (mARC) enzyme. The results show that a paramagnetic Mo(V) species is generated when reduced enzyme is exposed to nitrite, and an analysis of the resulting EPR hyperfine parameters confirms that mARC is remarkably similar to the low-pH form of sulfite oxidase. Two mechanisms for nitrite reduction have been considered. The first shows a modest reaction barrier of 14 kcal/mol for the formation of ·NO from unprotonated nitrite substrate. In marked contrast, protonation of the substrate oxygen proximal to Mo in the Mo(IV)-O-N-O substrate-bound species results in barrierless conversion to products. A fragment orbital analysis reveals a high degree of Mo-O(H)-N-O covalency that provides a π-orbital pathway for one-electron transfer to the substrate and defines orbital constraints on the Mo-substrate geometry for productive catalysis in mARC and other pyranopterin molybdenum enzymes that catalyze this one-electron transformation.
authors.affiliation: †Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States.
authors.forename: Jing
authors.initials: J
authors.lastname: Yang
authors.affiliation: †Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States.
authors.forename: Logan J
authors.initials: LJ
authors.lastname: Giles
authors.affiliation: ‡Department of Plant Biology, Braunschweig University of Technology, Humboldtstrasse 1, 38023 Braunschweig, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Ruppelt
authors.affiliation: ‡Department of Plant Biology, Braunschweig University of Technology, Humboldtstrasse 1, 38023 Braunschweig, Germany.
authors.forename: Ralf R
authors.initials: RR
authors.lastname: Mendel
authors.affiliation: ‡Department of Plant Biology, Braunschweig University of Technology, Humboldtstrasse 1, 38023 Braunschweig, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Bittner
authors.affiliation: †Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States.
authors.forename: Martin L
authors.initials: ML
authors.lastname: Kirk
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004579:Electron Transport; D017665:Hydroxyl Radical / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D008958:Models, Molecular; D008982:Molybdenum / Q000737:chemistry / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D050876:Sulfite Oxidase / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D009573:Nitrites; D017665:Hydroxyl Radical; D008982:Molybdenum; D010088:Oxidoreductases; C000605937:pmARC-2 protein, Arabidopsis; D050876:Sulfite Oxidase