Protons migrate along interfacial water without significant contributions from jumps between ionizable groups on the membrane surface

Abstract

Kinetics of fluorescence changes on top of three different lipid bilayers due to lateral proton migration. The observation area was located at a distance of 70 μm from the area of proton release. Because all FPE molecules are surrounded by DPhPC or DPhPE molecules, they are anticipated to accept protons, which are released from these molecules. GMO does not possess ionizable moieties so that in case of two-dimensional diffusion, proton release from one FPE molecule seems to be required before the next FPE molecule may pick up the proton. Despite the huge differences in proton release rates from the different lipids, τ max for all three lipid bilayers was similar. That is, lateral proton diffusivity is independent of the choice of the lipid. The buffer contained 0.1 mM Capso (pH 9.0) and 100 mM NaCl. The F1 Wv/+ mice were then backcrossed to A/J mice for 10 generations, creating A/J N10 Wv/+ mice. These were then crossed to B6 Wv/+ mice to create F1 wildtype and F1 Wv/Wv mice for study. A/J mice had an increased airway resistance compared to B6 mice, and F1 mice had a naïve AHR phenotype equivalent to their parental A/J strain. F1 Wv/Wv mice displayed an airway resistance similar to normoresponsive B6 mice. Values represent mean ± SE, n = at least 10 in each group.

Water at hydrophobic interfaces delays proton surface-to-bulk transfer and provides a pathway for lateral proton diffusion

“…Moreover, lateral diffusion along those bilayers persisted upon removal of titrable lipid groups. In the presence of such groups, D appeared to depend only weakly on their pK (9). The observed size of the isotope effect strongly supported the conclusion that the protons may travel along surface bound water (9).…”

“…If the proton would face a barrier upon approaching the interface from the bulk water, proton microinjection ( Fig. 1) would not result in surface diffusion spans and mobilities that are comparable to those obtained upon proton photo-release from the hydrophobic interface (8,9).…”

Superresolution microscopy reveals spatial separation of UCP4 and F 0 F 1 -ATP synthase in neuronal mitochondria

“…Thus, despite their different localization inside the mitochondria, all proteins would experience the same pmf. However, an increasing amount of evidence implies that protons do not easily equilibrate between the membrane surface and the bulk because of the presence of an energy barrier that has recently been quantified (29,30). It suggests that proton uptake (or release) transpires at the membrane surface (31) and does not occur from the bulk of the mitochondrial matrix or the bulk of the intermembrane space.…”

Single-file transport of water through membrane channels

“…6 Yet another example is provided by the water assisted movement of protons at solid surfaces 7,8 or along membranes. [9][10][11] In contrast to hydrophilic substances, water reduces the number of hydrogen bonds adjacent to extended hydrophobic substrates. 12 As a result, the rst layer of water molecules retracts from the surface -adopting a vapor-like structure.…”