title: Exchangeable oxygens in the vicinity of the molybdenum center of the high-pH form of sulfite oxidase and sulfite dehydrogenase.
abstract: The electron spin echo envelope modulation (ESEEM) investigation of the high-pH (hpH) form of sulfite oxidase (SO) and sulfite dehydrogenase (SDH) prepared in buffer enriched with H(2)(17)O reveals the presence of three types of exchangeable oxygen atoms at the molybdenum center. Two of these oxygen atoms belong to the equatorial OH ligand and the axial oxo ligand, and are characterized by (17)O hyperfine interaction (hfi) constants of about 37 MHz and 6 MHz, respectively. The third oxygen has an isotropic hfi constant of 3-4 MHz and likely belongs to a hydroxyl moiety hydrogen-bonded to the equatorial OH ligand. This exchangeable oxygen atom is not observed in the ESEEM spectra of the Y236F mutant of SDH, where the active site tyrosine has been replaced by phenylalanine.
authors.affiliation: Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA. andrei@u.arizona.edu
authors.forename: Andrei V
authors.initials: AV
authors.lastname: Astashkin
authors.forename: Eric L
authors.initials: EL
authors.lastname: Klein
authors.forename: Dmitry
authors.initials: D
authors.lastname: Ganyushin
authors.forename: Kayunta
authors.initials: K
authors.lastname: Johnson-Winters
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
authors.forename: Ulrike
authors.initials: U
authors.lastname: Kappler
authors.forename: John H
authors.initials: JH
authors.lastname: Enemark
mesh_terms: D020561:Alphaproteobacteria / Q000201:enzymology; D019943:Amino Acid Substitution; D000818:Animals; D020134:Catalytic Domain; D002645:Chickens; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008982:Molybdenum / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010103:Oxygen Isotopes / Q000737:chemistry; D050902:Sulfite Dehydrogenase / Q000737:chemistry*; D050876:Sulfite Oxidase / Q000737:chemistry*; D014443:Tyrosine / Q000737:chemistry
chemical_list: D010103:Oxygen Isotopes; D014443:Tyrosine; D008982:Molybdenum; D050902:Sulfite Dehydrogenase; D050876:Sulfite Oxidase; D010100:Oxygen