![transformed [Fe3Fe-4S] cluster in Desulfovibrio africanus FdIII, as observed by increasing the scan rate. The protein is adsorbed to approximately mono-layer coverage on an edge-oriented pyrolytic graphite electrode, using neomycin as coadsorbate, and the electrolyte contains 0.2M NaCl at pH 8.0, with 0.1 mM Fe(II). Temperature 0°C.](https://images.tandf.co.uk/common/jackets/crclarge/978082470/9780824707316.jpg "transformed [Fe3Fe-4S] cluster in Desulfovibrio africanus FdIII, as observed by increasing the scan rate. The protein is adsorbed to approximately mono-layer coverage on an edge-oriented pyrolytic graphite electrode, using neomycin as coadsorbate, and the electrolyte contains 0.2M NaCl at pH 8.0, with 0.1 mM Fe(II). Temperature 0°C.")
ABSTRACT
The film voltammetry experiment readily enables us to visualize this gating, since the cycle predominantly turns clockwise, with electrochemical energy being used to drive ligand transfer. Hypothetically, if one could energize the system instead by enforcing unfavorable ligand binding (for example, by mechanically inducing a conformational change or hydrolyzing ATP), then this energy would be conserved as a negative potential shift, thus providing an increased driving force for reduction processes. In this example, the exo-thiolate ligated cluster [Fe3Fe-4S]1+-L is a much stronger reductant than [Fe3Fe4S]1+, and preparing a sample for EPR characterization was not feasible due to the very high concentration of thiol required. Film voltammetry thus detects and records a cluster species (the “+” oxidation level) that cannot exist under normal conditions.
