pH dependence of proton translocation by Escherichia coli.
Proton translocation in spheroplasts from Escherichia coli has been studied in two mutants, one of which expresses cytochrome o and the other cytochrome d as the terminal oxidase. Using the O2 pulse method, the H+/e- ratio of proton translocation associated with cytochrome o was confirmed to be near 2 at neutral pH, but was found to decrease considerably when the medium pH was raised above 8. At high pH there was an increase in H+/OH- permeability of the cell membrane, but this was not sufficient to explain the decline in proton ejection. The pH effect was confined to cytochrome o-linked activity. It was not present when cytochrome d generated the electrochemical proton gradient. This makes it improbable that the Na+/H+ antiporter is responsible. The most likely explanation for our finding is that there is a "slip" in the proton-pumping mechanism of cytochrome o at high pH.
Verkhovskaya
M
M
Department of Medical Chemistry, University of Helsinki, Finland.
Verkhovsky
M
M
Wikström
M
M
D003573:Cytochrome b Group; D017937:Cytochrome d Group; D003580:Cytochromes / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D006863:Hydrogen-Ion Concentration; D010100:Oxygen / Q000378:metabolism; D011522:Protons; D013104:Spheroplasts / Q000378:metabolism
D003573:Cytochrome b Group; D003580:Cytochromes; D029968:Escherichia coli Proteins; D011522:Protons; D017937:Cytochrome d Group; C017168:cytochrome bo, E coli; D010100:Oxygen