The proton pump at work

Lateral proton conduction along a lipid-water interface layer: a molecular mechanism for the role of hydration water molecules

Using a fluorescence method applied to phospholipids spread at the air-water interface, we showed the occurrence of a localized proton pathway along the phospholipid polar heads. From the systematic investigation of this phenomenon, we conclude that the protons diffuse through a hydrogen bond network which is a matrix of hydrated polar head groups.

Lateral proton conduction at a lipid/water interface. Effect of lipid nature and ionic content of the aqueous phase

Fast lateral proton conduction was observed along the lipid/water interface using a fluorescence technique. This conduction can be detected for a large number of lipids, both phospholipids and glycolipids. The efficiency of the proton transfer is dependent on the molecular packing of the host lipid at a given surface pressure. The proton conduction which is present in the liquid expanded state is abolished by the transition to the liquid condensed state. The proton transfer is affected slightly by the ionic content of the aqueous subphase except in the case of calcium which can inhibit the conduction along phosphatidylglyceroethanolamine. We suggest that the transfer of the protons occurs along a bidimensional hydrogen-bond network formed from the polar head groups, their water molecules of hydration and the water molecules which are intercalated between the lipid molecules.