Directional Proton Transfer in Membrane Proteins Achieved through Protonated Protein‐Bound Water Molecules: A Proton Diode

While proton transfer in liquid water is random, membrane proteins creating the proton gradient for ATP synthesis perform a directional proton transfer via protein-bound protonated water molecules. This was shown in bacteriorhodopsin by a combination of time-resolved FTIR spectroscopy, X-ray crystallography, and molecular dynamics simulations.