The role of water and proton-transfer processes in hydrogen-bonded chains with large proton polarizability

The conditions under which hydrogen-bonded chains show large proton polarizability due to collective proton motion are discussed on the basis of theoretical as well as experimental results. These chains are very suitable pathways for the conduction of protons, since they can easily be regulated by electric fields. Three such pathways present in biological systems are discussed in which water molecules are believed to play an important role: (1) the proton-conducting system in the bacteriorhodopsin molecule; (2) the proton pathway in the F-0 subunit of ATP synthase; (3) the proton pathway in the enzyme alcohol dehydrogenase.