Spectroscopic studies of cobalt-substituted ferredoxin fromClostridium pasteurianum |
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Authors: | Lars Skjeldal Kristoffer K Andersson David Grace Torbjørn Ljones |
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Institution: | (1) Department of Chemistry, University of Trondheim, N-7055 Dragvoll, Norway;(2) Department of Biophysics, Arrhenius Laboratory, University of Stockholm, S-10691 Stockholm, Sweden;(3) Department of Biochemistry, University of Bergen, N-5009 Bergen, Norway;(4) Department of Chemistry, University of Oslo, 1 Oslo, Norway |
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Abstract: | Summary Ferredoxin fromClostridium 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 withg 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(Il)-thiolate coordination, which shifted dramatically upon exposure to air. The1H-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. |
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Keywords: | Ferredoxin Clostridium pasteurianum Cobalt derivative ERP NMR |
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