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J. Biol. Chem., Vol. 267, Issue 21, 14559-14562, Jul, 1992

pH dependence of proton translocation by Escherichia coli

M Verkhovskaya, M Verkhovsky and M Wikstrom
Department of Medical Chemistry, University of Helsinki, Finland.

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.
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				M. L. Verkhovskaya, A. Garcia-Horsman, A. Puustinen, J.-L. Rigaud, J. E. Morgan, M. I. Verkhovsky, and M. Wikstrom Glutamic acid 286 in subunit I of cytochrome bo3 is involved in proton translocation PNAS, September 16, 1997; 94(19): 10128 - 10131. [Abstract] [Full Text] [PDF]