Direct electrochemical oxidation of Clostridium pasteurianum ferredoxin: Identification of facile electron-transfer processes relevant to cluster degradation |
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Authors: | FA Armstrong HAO Hill NJ Walton |
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Institution: | Inorganic Chemistry Laboratory, University of Oxford, Oxford, OX1 3QR, England |
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Abstract: | Rapid oxidation processes relevant to the degradation of 4Fe4S] clusters in Clostridium pasteurianum ferredoxin were studied via direct (unmediated) heterogeneous electron transfer at a pyrolytic graphite electrode. Differential-pulse voltammograms of native 4Fe4S] ferredoxin showed two well-defined oxidation peaks corresponding to apparent E-values of +793 and +1120 mV at 5°C. Direct involvement of the cluster was established through parallel experiments with the 24Fe4Se] derivative for which peak positions were shifted. Square-wave voltammetry showed that the product of the first electron transfer, which may correspond to the ‘super-oxidised’ 4Fe4S]3+ oxidation level, undergoes rapid degradation (t < 1.6 ms at 5°C). The second oxidation process, as characterised by a significant (?100 mV) negative shift upon selenium substitution, very likely represents oxidation of S(Se) still associated with the protein and possibly contained within the remaining FES(Se) substructure. |
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Keywords: | Iron—Sulphur Ferredoxin Electrochemistry Super-oxidation Cluster degradation Pulse voltammetry |
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