Spectroscopic studies of cobalt-substituted ferredoxin from Clostridium pasteurianum.
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.
Skjeldal
L
L
Department of Chemistry, University of Trondheim, Dragvoll, Norway.
Andersson
K K
KK
Grace
D
D
Ljones
T
T
D003013:Clostridium / Q000032:analysis*; D003035:Cobalt; D004578:Electron Spin Resonance Spectroscopy; D005288:Ferredoxins / Q000302:isolation & purification*; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction
D005288:Ferredoxins; D003035:Cobalt