Evidence for reversible multiple redox transformations of [3Fe‐4S] clusters

Abstract

Analysis of the diffusionless cyclic voltammetry of ferredoxin III from Desulfovibrio africanus, co‐adsorbed with neomycin as an electroactive film on pyrolytic graphite ‘edge’ electrodes, shows that the reduced [3Fe‐4S]⁰ cluster undergoes further fast, chemically reversible, two‐electron reduction, at a potential E ⁰' = ca. −720 mV (pH 7.15, 0°C). The pH dependence of E ⁰' (pH 6.25–7.80) indicates net transfer of two H⁺. Observation of similar voltammetric waves in other proteins specifically containing [3Fe‐4S] centres suggests that extensive redox activity and stabilisation of what is formally an all‐Fe(II) species, may be a common, perhaps characteristic, feature of this cluster type.