New experimental evidence challenges the long-held paradigm of dynamical control in electrochemical protein electron transfer

Abstract

Over the past 30 years, electrochemical studies of redox proteins immobilized on functionalized electrodes have consistently shown that electron transfer rate constants () vary exponentially with electrode-protein distance at long separations, but reportedly reach a plateau and become viscosity-dependent at shorter distances. This behaviour led to different hypotheses suggesting either a shift from a non-adiabatic to friction-controlled ET regime or a gating rate-limiting step, with implications for biological ET in crowded cellular environments and bioelectronics. Here, we demonstrate for three different metalloproteins that this plateau results from uncompensated resistance in the electrochemical cell and that itself remains exponential across all distances tested, from 6 to 20 Å, consistent with the contemporary ET theory. The previously observed dependencies of on viscosity and temperature, once considered indicative of gating or friction-controlled ET, are also shown to stem from uncompensated resistance. These findings compel us to reassess our understanding of electrochemical protein electron transfer.