Interfacial proton diffusion

Description

Protons drive (i) ATP synthesis and (ii) protein translocation across the bacterial plasma membrane. These processes may persist, even if the bulk pH difference between the solutions on both sides of the membrane is too small to serve as an energy source. Lateral proton diffusion from the proton pump towards the ATP synthase or the translocon is believed to provide an explanation. Proton migration along the membrane is commonly regarded as a succession of jumps between membrane-anchored proton binding sites. Our experiments provide evidence for an alternative model. We released protons at the interface and monitored their arrival at distant sites by fluorescence measurements. The kinetics of the arrival was probed as a function of distance (i) for membranes of various compositions [1] and (ii) for the decane/water interface [2]. We found that long-range proton diffusion along the interface required neither the presence of ionizable groups [1] nor polar groups [2]. It persisted even after the complete removal of lipids [2]. Salt removal altered the diffusion constant of 5x10-6 cm2 s-1, but did not inhibit long-range lateral proton migration. Surface-to-bulk transfer was delayed by an energy barrier, which according to measurements at various temperatures amounted to at least 8.7 kT [2]. The observation of a large isotope effect supported the conclusion that interfacial water provided the pathway for rapid lateral proton migration.

Period	25 Sept 2012
Event title	Annual Meeting of the German Biophysical Society
Event type	Conference
Location	GermanyShow on map