The final product of cellular respiration is the proton motive force, formed by protons pumped out of the membrane and by the voltage due to all charges. While Mitchell’s original theory considered pumped protons released immediately to the bulk external medium, that has been criticized. Today there is a good amount of research showing that protons tend to remain confined in 2D in proximity with the membrane (one review can be found here). This would explain how certain extremophiles can survive in very basic niches (poor in protons), where the proton motive force, defined from the bulk pH, cannot sustain ATP synthesis.
As far as I have been able to discover, the existence of such “surface protons” has only been shown in vitro (e.g. in a sustained lipid bilayer).
Is there any experimental evidence of such “surface protons” in intact cells, i.e. in vivo?