Long-Range Electron Transfer in Biology

Abstract

Electron‐transfer processes are vital elements of energy transduction pathways in living cells. A unique synergy between theory and experiment has produced an extraordinarily detailed understanding of the factors that regulate this ‘current of life’. Studies of Ru‐modified proteins have provided insights into the distance‐ and driving‐force dependences of intraprotein electron transfer rates. Electron transfer across protein–protein interfaces has been probed both in solution and in structurally characterized crystals. It is now clear that electrons tunnel between sites in biological redox chains, and that protein structures tune thermodynamic properties and electronic coupling interactions to facilitate these reactions. This research has produced an experimentally validated, electron tunneling timetable that predicts the time required for an electron to transfer across a specified distance in a protein. Many of the electron tunneling rates measured in cytochrome c oxidase and photosynthetic reaction centers agree well with timetable predictions, indicating that the natural reactions are highly optimized, both in terms of thermodynamics and electronic coupling.