title: A quantum-mechanical study of the reaction mechanism of sulfite oxidase.
abstract: The oxidation of sulfite to sulfate by two different models of the active site of sulfite oxidase has been studied. Both protonated and deprotonated substrates were tested. Geometries were optimized with density functional theory (TPSS/def2-SV(P)) and energies were calculated either with hybrid functionals and large basis sets (B3LYP/def2-TZVPD) including corrections for dispersion, solvation, and entropy, or with coupled-cluster theory (LCCSD(T0)) extrapolated toward a complete basis set. Three suggested reaction mechanisms have been compared and the results show that the lowest barriers are obtained for a mechanism where the substrate attacks a Mo-bound oxo ligand, directly forming a Mo-bound sulfate complex, which then dissociates into the products. Such a mechanism is more favorable than mechanisms involving a Mo-sulfite complex with the substrate coordinating either by the S or O atom. The activation energy is dominated by the Coulomb repulsion between the Mo complex and the substrate, which both have a negative charge of -1 or -2.
authors: Theoretical Chemistry, Department of Chemistry, Chemical Centre, Lund University, P. O. Box 124, 221 00, Lund, Sweden.
authors: Marie-Céline
authors: MC
authors: van Severen
authors: Milica
authors: M
authors: Andrejić
authors: Jilai
authors: J
authors: Li
authors: Kerstin
authors: K
authors: Starke
authors: Ricardo A
authors: RA
authors: Mata
authors: Ebbe
authors: E
authors: Nordlander
authors: Ulf
authors: U
authors: Ryde
mesh_terms: D000818:Animals; D002645:Chickens; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008982:Molybdenum / Q000378:metabolism*; D010084:Oxidation-Reduction; D011789:Quantum Theory; D013431:Sulfates / Q000378:metabolism; D050876:Sulfite Oxidase / Q000737:chemistry / Q000378:metabolism*; D013447:Sulfites / Q000378:metabolism
chemical_list: D013431:Sulfates; D013447:Sulfites; D008982:Molybdenum; D050876:Sulfite Oxidase