Temperature-driven changeover in the electron-transfer mechanism of a thermophilic plastocyanin

Abstract

Electron-transfer kinetics of the thermophilic protein Plastocyanin fromPhormidium laminosumadsorbed on 1,ω-alkanedithiol self-assembled monolayers (SAMs)deposited on gold have been investigated. The standard electron-transfer rate constant hasbeen determined as a function of electrode−protein distance and solution viscosity over abroad temperature range (0−90°C). For either thin or thick SAMs, the electron-transferregime remains invariant with temperature, whereas for the 1,11-undecanethiol SAM ofintermediate chain length, a kinetic regime changeover from a gated or friction-controlledmechanism at low temperature (0−30°C) to a nonadiabatic mechanism above 40°Cisobserved. To the best of our knowledge, this is thefirst time a thermal-induced transitionbetween these two kinetic regimes is reported for a metalloprotein.