title: Spectroscopic studies of cobalt-substituted ferredoxin from Clostridium pasteurianum.
abstract: Ferredoxin from Clostridium pasteurianum substituted with two Co atoms did not give any cobalt EPR signal at 8 K as isolated, but upon reduction with sodium dithionite, a broad signal appeared with g values that indicate highspin (S = 3/2) Co(II). These signals were distinct from Co(II)-dithiothreitol signals, and disappeared upon reoxidation with air. Under anaerobic incubation of apoferredoxin with Co(II), a green derivative showed a visible spectrum typical of tetrahedral Co(II)-thiolate coordination, which shifted dramatically upon exposure to air. The 1H-NMR spectrum of the aerobically isolated protein is reported at 300 MHz; magnetic susceptibility measurements were indicative of a diamagnetic species. These spectroscopic studies indicate that Co(II)-substituted ferredoxin is oxidized to low-spin Co(III)-ferredoxin in the presence of sulfide and oxygen. The diamagnetic Co(III) state could reversibly be reduced to highspin Co(II) by sodium dithionite.
authors.affiliation: Department of Chemistry, University of Trondheim, Dragvoll, Norway.
authors.forename: L
authors.initials: L
authors.lastname: Skjeldal
authors.forename: K K
authors.initials: KK
authors.lastname: Andersson
authors.forename: D
authors.initials: D
authors.lastname: Grace
authors.forename: T
authors.initials: T
authors.lastname: Ljones
mesh_terms: D003013:Clostridium / Q000032:analysis*; D003035:Cobalt; D004578:Electron Spin Resonance Spectroscopy; D005288:Ferredoxins / Q000302:isolation & purification*; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction
chemical_list: D005288:Ferredoxins; D003035:Cobalt