PMID:15339819

Citation	Franklin, MJ, Brusilow, WS and Woodbury, DJ (2004) Determination of proton flux and conductance at pH 6.8 through single FO sectors from Escherichia coli. Biophys. J. 87:3594-9
Abstract	We have developed a mathematical model in concert with an assay that allows us to calculate proton (H+) flux and conductance through a single FO of the F1FO ATP synthase. Lipid vesicles reconstituted with just a few functional FO from Escherichia coli were loaded with 250 mM K+ and suspended in a low K+ solution. The pH of the weakly buffered external solution was recorded during sequential treatment with the potassium ionophore valinomycin, the protonophore carbonyl cyanide 3-chlorophenylhydrazone, and HCl. From these pH traces and separate determinations of vesicle size and lipid concentration we calculate the proton conductance through a single FO sector. This methodology is sensitive enough to detect small (15%) conductance changes. We find that wild-type FO has a proton flux of 3100 +/- 500 H+/s/FO at a transmembrane potential of 106 mV (25 degrees C and pH 6.8). This corresponds to a proton conductance of 4.4 fS.
Links	PubMed PMC1304824 Online version:10.1529/biophysj.104.044248
Keywords	Algorithms; Electric Conductivity; Escherichia coli/enzymology; Hydrogen-Ion Concentration; Ion Channel Gating; Liposomes/chemistry; Models, Chemical; Proton-Translocating ATPases/analysis; Proton-Translocating ATPases/chemistry; Protons
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