Abstract
The decaheme cytochrome MtrC from Shewanella oneidensis MR-1 immobilized on an ITO electrode displays unprecedented H2O2 reduction activity. Although MtrC showed lower peroxidase activity in solution compared to horseradish peroxidase, the ten heme cofactors enable excellent electronic communication and a superior activity on the electrode surface. A hierarchical ITO electrode enabled optimal immobilization of MtrC and a high current density of 1 mA cm–2 at 0.4 V vs SHE could be obtained at pH 6.5 (Eonset = 0.72 V). UV–visible and Resonance Raman spectroelectrochemical studies suggest the formation of a high valent iron-oxo species as the catalytic intermediate. Our findings demonstrate the potential of multiheme cytochromes to catalyze technologically relevant reactions and establish MtrC as a new benchmark in biotechnological H2O2 reduction with scope for applications in fuel cells and biosensors.
Highlights
Suggested to be responsible for its activity.[15]
MtrC is a decaheme protein and part of the protein complex MtrCAB that can be found in the outer membrane of Shewanella oneidensis MR-1.17 Within the organism, MtrCAB is known to act as an electron conduit from the intracellular to the extracellular environment, where MtrC can transfer electrons to different acceptors, such as metal oxides and flavins.[18]
E lectrocatalytic conversion of H2O2 has been extensively studied toward the development ofsensors.[1]
Summary
At more negative potentials new signals at 419, 524, and 552 nm appeared, corresponding to the formation of the reduced FeII-hemes in MtrC.[20] The disappearance of FeIII-heme bands at E < −0.35 V indicates that the majority of heme cofactors in the adsorbed. Addition of H2O2 (5 mM) to the electrolyte solution caused a substantial increase of the open circuit potential (OCP) for the mesoITO|MtrC electrode from 0.37 to 0.75 V (Figure 3a), which is close to that reported for FeIV=O of peroxidase active sites and suggests the formation of a high oxidation state intermediate.[16] The free cofactor, hemin, and HRP were immobilized on mesoITO electrodes. Upon addition of H2O2, the OCP increased from 0.45 to 0.61 V for mesoITO|hemin (7.5 nmol hemin per cm[2]; Figure S3), and mesoITO|HRP showed only a modest increase from 0.42 to 0.46 V, probably due to unfavorable enzyme orientation (Figure 3a)
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