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p.11289 left column bottom paragraph:"In most bacterial cells, the antiporter is the major Na+-extruding mechanism driven by the inwardly directed H+-
electrochemical gradient. In contrast to the human protein, which is electroneutral, the bacterial one is electrogenic with an overall stoichiometry of H+ to Na+ above 1 (Schuldiner and Fishkes, 1978 Castle et al., 1986 & primary source), and it is activated by alkaline rather than acid pH (Leblanc et al., 1988). The overall apparent stoichiometry was measured over a wide pH range. It was shown that the stoichiometry changes from 1.1 at pH 7.4 to 1.3 at pH 7.8 and reaches 1.4 at pH 8.4 (primary source Pan & Macnab). Macnab and collaborators
suggest the possible existence of two antiporters, one electroneutral and the other electrogenic with a stoichiometry (H+:Na+) of 2, which when functioning together, yield the apparent nonintegral stoichiometry (Castle et al., 1986 & primary source)." |