title: Electronic properties of the dissimilatory sulphite reductase from Desulfovibrio vulgaris (Hildenborough): comparative studies of optical spectra and relative reduction potentials for the [Fe4S4]-sirohaem prosthetic centres.
abstract: The dissimilatory sulphite reductase (desulfoviridin) from the sulphate-reducing bacterium Desulfovibrio vulgaris (Hildenborough) displays distinct optical and redox characteristics relative to the haem subunit of Escherichia coli assimilatory sulphite reductase. For high-spin pentaco-ordinate desulfoviridin there is minimal change in the absorbance of the oxidized chromophores both after reduction or after addition of exogenous ligands. A ligand-metal charge-transfer band approximately 702 nm is observed in both the oxidized and one-electron-reduced enzyme. E.p.r. spectroscopy has been used to define the relative reduction potentials for sirohaem and [Fe4S4] centres (delta E0 = Es0-Ec0) as a function of sirohaem axial co-ordination. Typically delta E0 lies in a range from -10 to -50 mV. These results show a correlation with the sigma-donor or pi-acceptor properties of the ligand and stand in sharp contrast with estimates for the E. coli enzyme. The electronic properties of the coupled [Fe4S4]-sirohaem redox centre common to both nitrite- and sulphite-reducing enzymes are apparently strongly dependent on the environment generated by protein side chains.
authors.affiliation: Evans Laboratory of Chemistry, Ohio State University, Columbus 43210.
authors.forename: S M
authors.initials: SM
authors.lastname: Lui
authors.forename: A
authors.initials: A
authors.lastname: Soriano
authors.forename: J A
authors.initials: JA
authors.lastname: Cowan
mesh_terms: D001665:Binding Sites; D016969:Desulfovibrio vulgaris / Q000201:enzymology*; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000201:enzymology; D006418:Heme / Q000737:chemistry; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000737:chemistry*
chemical_list: D007506:Iron-Sulfur Proteins; D006418:Heme; D050862:Oxidoreductases Acting on Sulfur Group Donors