Proton conductance by the gramicidin water wire. Model for proton conductance in the F1F0 ATPases?
The gramicidin channel contains a single strand of water molecules associated through hydrogen bonds. Previous work has shown that channels of similar size are formed by association of transmembrane alpha helices of synthetic leucine-serine peptides. Both types of channels translocate protons with considerable selectivity relative to other cations, and it has been proposed that the selectivity arises by proton "hopping" along hydrogen-bonded chains of water, whereas other cations must cross by ordinary diffusion processes. It is possible that a similar mechanism underlies proton transport in the Fo subunit of the F1F0 ATP synthase. Using the gramicidin channel as a model, we have tested whether a single strand of water is kinetically competent to translocate protons at a rate sufficient to support known rates of ATP synthesis. We found that the gramicidin channel saturates at approximately 530 pS of protonic current in 4 M HCl, more than sufficient for typical ATP synthesis rates. It follows that proton diffusion to a putative channel in Fo, rather than the channel itself, may limit ATP synthesis rates.
Akeson
M
M
Department of Zoology, University of California, Davis 95616.
Deamer
D W
DW
D006096:Gramicidin; D006851:Hydrochloric Acid; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007473:Ion Channels / Q000502:physiology*; D008051:Lipid Bilayers; D008564:Membrane Potentials; D008954:Models, Biological; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D011522:Protons; D013816:Thermodynamics
D007473:Ion Channels; D008051:Lipid Bilayers; D011522:Protons; D006096:Gramicidin; D006180:Proton-Translocating ATPases; D006851:Hydrochloric Acid