title: High-resolution EXAFS of the active site of human sulfite oxidase: comparison with density functional theory and X-ray crystallographic results.
abstract: Much of our knowledge about molybdenum enzymes has originated from EXAFS spectroscopy. This technique provides excellent bond-length accuracy but has only limited bond-length resolution. We have used EXAFS spectroscopy with an extended data range in an attempt to improve bond-length resolution for the molybdenum enzyme sulfite oxidase. The Mo site of sulfite oxidase has two oxygen and three Mo-S ligands (two from cofactor dithiolene plus a cysteine). For the oxidized (Mo(VI)) enzyme, we find that the three Mo-S bond lengths are very similar (within 0.05 A) at 2.41 A, as are the Mo=O ligands at 1.72 A. Density functional theory shows that this is consistent with the proposed active-site structure. The reduced (Mo(IV)) enzyme shows two Mo-S bond lengths at 2.35 A and one at 2.41 A (assigned to cofactor dithiolene and cysteine, respectively, from DFT), together with one Mo=O at 1.72 A and one Mo-OH(2) at 2.30 A.
authors.affiliation: School of Chemistry, University of Sydney, New South Wales 2006, Australia.
authors.forename: Hugh H
authors.initials: HH
authors.lastname: Harris
authors.forename: Graham N
authors.initials: GN
authors.lastname: George
authors.forename: K V
authors.initials: KV
authors.lastname: Rajagopalan
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray; D006801:Humans; D008956:Models, Chemical; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis / Q000379:methods; D050876:Sulfite Oxidase / Q000737:chemistry*; D014965:X-Rays
chemical_list: D050876:Sulfite Oxidase