The kinetics of a weakly electron-coupled proton transfer in azurin

The thermodynamics and kinetics of the weakly electron-coupled proton transfer of Pseudomonas aeruginosa azurin have been studied and quantitatively determined using fast scan cyclic voltammetry (CV), in which the protein is adsorbed on two types of electrode (pyrolytic graphite ‘edge’ (PGE) or 1-decanethiol modified gold). Electron transfer is coupled to a slow protonation of His35, which is not a ligand to the copper ion but is located approximately 8 Å away. Protonation of His35 produces small changes in the reduction potential of the copper site, which are time-resolved within the scan rate range 0.01–100 V s−1.