Directional electron transfer from ubiquinone-10 to cytochrome c at a biomimetic self-assembled monolayer modified electrode

Abstract

The redox behavior of cytochrome c (Cyt c) at a ubiquinone-10 (UQ) incorporated self-assembled monolayer (SAM)-modified electrode was studied by cyclic voltammetry. A well-defined catalytic wave due to the reduction of Cyt c by UQ was observed at around −0.4 V vs. Ag/AgCl (saturated KCl). However, the re-oxidation peak of UQ at around +0.3 V was small, suggesting no significant catalytic ability of UQ for the re-oxidation of Cyt c. These voltammetric behaviors could be well simulated by digital simulation with a simple reaction model in which UQ and Cyt c coexist homogeneously in a reaction layer on the base gold electrode. The parameters obtained by curve fitting of cyclic voltammograms showed that the re-oxidation of Cyt c by UQ is somewhat thermodynamically unfavorable and, importantly, kinetically slow. This slow process is probably originated from spatial separation between the redox species. Such a directional or one-way electron transfer may be occurring in the mitochondrial respiratory chain system to achieve efficient energy production.