The Problem of Proton Transfer in Membranes

Proton (H+) transfer has been examined in many molecular systems for more than 50 years. General mechanistic possibilities including tunnelling have been recognized for proton movement from local base-to-base centres. An especially fast mechanism over considerable distances, the Grotthus mechanism, has been described in water. Proton transfer over long distances in membranes which is now known to occur in many protein bio-energetic devices is not understood since ground state structures do not provide a continuous H-bond network. Here we consider the possible mechanisms and propose that the most likely pathway for protons in membranes uses an excited conformational state, equivalent to a partial denaturation.