The past and present of sodium energetics: may the sodium-motive force be with you.
All living cells routinely expel Na(+) ions, maintaining lower concentration of Na(+) in the cytoplasm than in the surrounding milieu. In the vast majority of bacteria, as well as in mitochondria and chloroplasts, export of Na(+) occurs at the expense of the proton-motive force. Some bacteria, however, possess primary generators of the transmembrane electrochemical gradient of Na(+) (sodium-motive force). These primary Na(+) pumps have been traditionally seen as adaptations to high external pH or to high temperature. Subsequent studies revealed, however, the mechanisms for primary sodium pumping in a variety of non-extremophiles, such as marine bacteria and certain bacterial pathogens. Further, many alkaliphiles and hyperthermophiles were shown to rely on H(+), not Na(+), as the coupling ion. We review here the recent progress in understanding the role of sodium-motive force, including (i) the conclusion on evolutionary primacy of the sodium-motive force as energy intermediate, (ii) the mechanisms, evolutionary advantages and limitations of switching from Na(+) to H(+) as the coupling ion, and (iii) the possible reasons why certain pathogenic bacteria still rely on the sodium-motive force.
Mulkidjanian
Armen Y
AY
School of Physics, University of Osnabrück, D-49069 Osnabrück, Germany. amulkid@uos.de
Dibrov
Pavel
P
Galperin
Michael Y
MY
D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D001693:Biological Transport, Active; D004734:Energy Metabolism; D008958:Models, Molecular; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D025262:Vacuolar Proton-Translocating ATPases / Q000737:chemistry / Q000378:metabolism
D021122:Protein Subunits; D012964:Sodium; D000251:Adenosine Triphosphatases; D025262:Vacuolar Proton-Translocating ATPases; D006180:Proton-Translocating ATPases