title: Coordination chemistry at the molybdenum site of sulfite oxidase: redox-induced structural changes in the cysteine 207 to serine mutant.
abstract: The redox chemistry of the molybdenum site of the C207S mutant of recombinant human sulfite oxidase has been studied via potentiometric titrations employing both electron paramagnetic resonance (EPR) spectroscopy and X-ray absorption spectroscopy (XAS) as probes of the active site structure. In earlier EXAFS studies, oxidized Cys207Ser enzyme has been shown to possess a novel tri-oxo active site, in which Ser207 does not appear to be a ligand to Mo [George, G. N.; Garrett, R. M.; Prince, R. C.; Rajagopalan, K. V. J. Am. Chem. Soc. 1996, 118, 8588-8592]. Redox titrations show that the active site is modified under reducing conditions to a mono-oxo Mo(IV) species, probably with Ser207 ligated to the metal. The Mo(IV) species can be reoxidized to a mono-oxo Mo(V) species still coordinated to Ser207, which in turn can be further reoxidized to yield the initial tri-oxo Mo(VI) structure with loss of Ser207 ligation.
authors.affiliation: Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada. g.george@usask.ca
authors.forename: Graham N
authors.initials: GN
authors.lastname: George
authors.forename: Robert M
authors.initials: RM
authors.lastname: Garrett
authors.forename: Roger C
authors.initials: RC
authors.lastname: Prince
authors.forename: K V
authors.initials: KV
authors.lastname: Rajagopalan
mesh_terms: D001665:Binding Sites; D003545:Cysteine / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D015394:Molecular Structure; D008982:Molybdenum / Q000737:chemistry*; D009154:Mutation; D010084:Oxidation-Reduction; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D012694:Serine / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D012694:Serine; D008982:Molybdenum; D050862:Oxidoreductases Acting on Sulfur Group Donors; D003545:Cysteine