Very rapid, cooperative two-electro/two-proton redox reactions of [3Fe- 4S] clusters: Detection and analysis by protein-film voltammetry

Abstract

The 'hyper-reduced' [3Fe-4S]2- cluster (consisting formally of three Fe(II) atoms and four sulfides (S2-)) possesses a remarkable capability for very rapid and reversible two-electron/two-proton oxidation (E(o') > -650 mv below pH 7) that is strongly suggestive of disulfide-based (as opposed to Fe- based) redox chemistry. This otherwise elusive reactivity is most readily revealed by performing fast-scan protein-film voltammetry on ferredoxins that contain a [3Fe-4S] cluster using an electrolyte composed of D2O. Fast, cooperative two-electron/two-proton transfer is observed after first generating the fully reduced [3Fe-4S]2- state and then cycling rapidly to more oxidizing potentials. The unu..