Stability, redox parameters and electrocatalytic activity of a cytochrome domain from a new subfamily

•The cytochrome c domain (Cyt-D) from R. marinus O2-reductase exhibits higher chemical stability than canonical cytochromes.•When adsorbed on SAM-coated electrodes, thermal stability is also higher.•The immobilized protein exhibits fast direct electron transfer with λ = 0.33 eV.•Cyt-D electrodes show electrocatalytic activity towards H2O2.

We report a spectroscopic, electrochemical and spectroelectrochemical characterization of the soluble cytochrome c domain (Cyt-D) from the Rhodothermus marinus caa3 terminal oxygen reductase and its putative electron donor, a high potential [4Fe–4S] protein (HiPIP). Cyt-D exhibits superior stability, particularly at the level of the heme pocket, compared to archetypical cytochromes in terms of thermal and chemical denaturation, alkaline transition and oxidative bleaching of the heme, which is further increased upon adsorption on biomimetic electrodes. Therefore, this protein is proposed as a suitable building block for electrochemical biosensing. As a proof of concept, we show that the immobilized Cyt-D exhibits good electrocatalytic activity towards H2O2 reduction. Relevant thermodynamic and kinetic electron transfer parameters for Cyt-D and HiPIP are also reported, including reorganization energies of 0.33 eV and 0.42 eV, respectively.

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