Reduction of dioxygen to water during the terminal step of aerobic respiration is triggered by electron transfer from ferrous cytochrome c (cyt c) into the oxidized binuclear [Cu(Cys)2Cu]+ core of the CuA domain of cytochrome c oxidase. Direct electrochemistry of a water-soluble fragment from the CuA domain of Thermus thermophilus cytochrome ba3 has revealed a reduction potential of 0.24 V vs. NHE; the corresponding potential of its biological partner, cytochrome c552 has been reported between 0.23 – 0.20 V vs. NHE under similar conditions. The rate of cyt c522-to-CuA electron transfer, ~ 105s-1, appears to be anomalously high given the modest driving force for the reaction as determined by solution electrochemistry, at least at the lower end of the range (ΔGo ~ -0.01 eV). Here we report thermodynamic parameters for the reduction of CuA and cyt c552 bound respectively to amine- and carboxylate-terminated alkylthiols on gold as a model for protein-protein interfacial electron transfer. Our data suggest that ΔGo for the interfacial reaction increases by more than ~ 30 meV as a consequence of surface binding. This binding-induced redox shift may play a role in the extremely rapid electron transfer rate from cyt c into cytochrome c oxidase.

Modeling cytochrome c552 / CuA interfacial electron transfer at gold electrodes modified with functionalized SAMs

2019 Spring National Meeting

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