title: Characterization of a sulfite reductase from Desulfovibrio vulgaris. Evidence for the presence of a low-spin siroheme and an exchange-coupled siroheme-[4Fe-4S] unit.
abstract: We have studied a low-molecular-weight (Mr = 27,200) sulfite reductase from Desulfovibrio vulgaris (Hildenborough, NCIB 8303) with Mössbauer, EPR, and chemical techniques. This sulfite reductase was found to contain one siroheme and one [4Fe-4S] cluster. As purified, the siroheme is low-spin ferric (S = 1/2) which exhibits characteristic EPR resonances at g = 2.44, 2.36, and 1.77. At 150 K, the observed Mössbauer parameters, delta EQ = 2.49 +/- 0.02 mm/s and delta = 0.31 +/- 0.02 mm/s, for the siroheme are typical for low-spin ferric complexes. The [4Fe-4S] cluster is in the 2+ state. The Mössbauer parameters, delta EQ = 0.95 +/- 0.02 mm/s and delta = 0.38 +/- 0.02 mm/s, for the cluster are almost identical to those observed for the [4Fe-4S]2+ cluster in the hemoprotein subunit of the sulfite reductase from Escherichia coli. Similar to the hemoprotein subunit of E. coli sulfite reductase, low-temperature Mössbauer spectra of D. vulgaris sulfite reductase recorded with weak and strong applied fields also show evidence for an exchange-coupled siroheme-[4Fe-4S] unit.
mesh_terms: D003901:Desulfovibrio / Q000201:enzymology*; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000031:analogs & derivatives* / Q000032:analysis; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D007700:Kinetics; D008667:Metalloproteins / Q000378:metabolism*; D008970:Molecular Weight; D010088:Oxidoreductases / Q000378:metabolism*; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000378:metabolism*; D013053:Spectrophotometry; D013057:Spectrum Analysis
chemical_list: D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D006418:Heme; C009272:siroheme; D010088:Oxidoreductases; D050862:Oxidoreductases Acting on Sulfur Group Donors