title: Sulfite Oxidase Catalyzes Single-Electron Transfer at Molybdenum Domain to Reduce Nitrite to Nitric Oxide.
abstract: OBJECTIVE
  Recent studies suggest that the molybdenum enzymes xanthine oxidase, aldehyde oxidase, and mARC exhibit nitrite reductase activity at low oxygen pressures. However, inhibition studies of xanthine oxidase in humans have failed to block nitrite-dependent changes in blood flow, leading to continued exploration for other candidate nitrite reductases. Another physiologically important molybdenum enzyme—sulfite oxidase (SO)—has not been extensively studied.
  
  
  RESULTS
  Using gas-phase nitric oxide (NO) detection and physiological concentrations of nitrite, SO functions as nitrite reductase in the presence of a one-electron donor, exhibiting redox coupling of substrate oxidation and nitrite reduction to form NO. With sulfite, the physiological substrate, SO only facilitates one turnover of nitrite reduction. Studies with recombinant heme and molybdenum domains of SO indicate that nitrite reduction occurs at the molybdenum center via coupled oxidation of Mo(IV) to Mo(V). Reaction rates of nitrite to NO decreased in the presence of a functional heme domain, mediated by steric and redox effects of this domain. Using knockdown of all molybdopterin enzymes and SO in fibroblasts isolated from patients with genetic deficiencies of molybdenum cofactor and SO, respectively, SO was found to significantly contribute to hypoxic nitrite signaling as demonstrated by activation of the canonical NO-sGC-cGMP pathway.
  
  
  METHODS
  Nitrite binds to and is reduced at the molybdenum site of mammalian SO, which may be allosterically regulated by heme and molybdenum domain interactions, and contributes to the mammalian nitrate-nitrite-NO signaling pathway in human fibroblasts.
  
  
  CONCLUSIONS
  SO is a putative mammalian nitrite reductase, catalyzing nitrite reduction at the Mo(IV) center.
authors.affiliation: 1 Pittsburgh Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh , Pittsburgh, Pennsylvania.|2 Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania.
authors.forename: Jun
authors.initials: J
authors.lastname: Wang
authors.affiliation: 3 Department of Biochemistry, Center for Molecular Medicine, Institute of Biochemistry, Cologne University , Cologne, Germany .
authors.forename: Sabina
authors.initials: S
authors.lastname: Krizowski
authors.affiliation: 3 Department of Biochemistry, Center for Molecular Medicine, Institute of Biochemistry, Cologne University , Cologne, Germany .
authors.forename: Katrin
authors.initials: K
authors.lastname: Fischer-Schrader
authors.affiliation: 4 Department of Biochemistry, University of California at Riverside , Riverside, California.
authors.forename: Dimitri
authors.initials: D
authors.lastname: Niks
authors.affiliation: 1 Pittsburgh Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh , Pittsburgh, Pennsylvania.|2 Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania.
authors.forename: Jesús
authors.initials: J
authors.lastname: Tejero
authors.affiliation: 1 Pittsburgh Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh , Pittsburgh, Pennsylvania.|2 Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania.
authors.forename: Courtney
authors.initials: C
authors.lastname: Sparacino-Watkins
authors.affiliation: 1 Pittsburgh Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh , Pittsburgh, Pennsylvania.|2 Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania.
authors.forename: Ling
authors.initials: L
authors.lastname: Wang
authors.affiliation: 1 Pittsburgh Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh , Pittsburgh, Pennsylvania.|2 Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania.
authors.forename: Venkata
authors.initials: V
authors.lastname: Ragireddy
authors.affiliation: 1 Pittsburgh Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh , Pittsburgh, Pennsylvania.|2 Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania.
authors.forename: Sheila
authors.initials: S
authors.lastname: Frizzell
authors.affiliation: 1 Pittsburgh Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh , Pittsburgh, Pennsylvania.|5 Department of Anesthesiology, University of Pittsburgh , Pittsburgh, Pennsylvania.
authors.forename: Eric E
authors.initials: EE
authors.lastname: Kelley
authors.affiliation: 2 Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania.
authors.forename: Yingze
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: 6 Department of Chemistry and Biochemistry, Duquesne University , Pittsburgh, Pennsylvania.
authors.forename: Partha
authors.initials: P
authors.lastname: Basu
authors.affiliation: 4 Department of Biochemistry, University of California at Riverside , Riverside, California.
authors.forename: Russ
authors.initials: R
authors.lastname: Hille
authors.affiliation: 3 Department of Biochemistry, Center for Molecular Medicine, Institute of Biochemistry, Cologne University , Cologne, Germany .
authors.forename: Guenter
authors.initials: G
authors.lastname: Schwarz
authors.affiliation: 1 Pittsburgh Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh , Pittsburgh, Pennsylvania.|2 Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh , Pittsburgh, Pennsylvania.
authors.forename: Mark T
authors.initials: MT
authors.lastname: Gladwin
mesh_terms: D003067:Coenzymes / Q000737:chemistry*; D004579:Electron Transport; D005347:Fibroblasts / Q000201:enzymology / Q000378:metabolism; D006418:Heme / Q000737:chemistry; D006801:Humans; D008667:Metalloproteins / Q000737:chemistry*; D008982:Molybdenum / Q000737:chemistry; D000090006:Molybdenum Cofactors; D009569:Nitric Oxide / Q000737:chemistry* / Q000378:metabolism; D009573:Nitrites / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D017434:Protein Structure, Tertiary; D011621:Pteridines / Q000737:chemistry*; D015398:Signal Transduction; D050876:Sulfite Oxidase / Q000737:chemistry* / Q000378:metabolism
chemical_list: D003067:Coenzymes; D006418:Heme; D008667:Metalloproteins; D008982:Molybdenum; D000090006:Molybdenum Cofactors; D009569:Nitric Oxide; D009573:Nitrites; D011621:Pteridines; D050876:Sulfite Oxidase; C022261:molybdopterin