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Journal of Experimental Biology, Vol 203, Issue 1 51-59, Copyright © 2000 by Company of Biologists

JOURNAL ARTICLES

Crucial role of the membrane potential for ATP synthesis by F(1)F(o) ATP synthases

P Dimroth, G Kaim and U Matthey
Institut fur Mikrobiologie, Eidgenossische Technische Hochschule, ETH-Zentrum, Schmelzbergstrasse 7, CH-8092 Zurich, Switzerland. dimroth@micro.biol.ethz.ch

ATP, the universal carrier of cell energy, is manufactured from ADP and phosphate by the enzyme ATP synthase using the free energy of an electrochemical gradient of protons (or Na(+)). The proton-motive force consists of two components, the transmembrane proton concentration gradient (delta pH) and the membrane potential. The two components were considered to be not only thermodynamically but also kinetically equivalent, since the chloroplast ATP synthase appeared to operate on delta pH only. Recent experiments demonstrate, however, that the chloroplast ATP synthase, like those of mitochondria and bacteria, requires a membrane potential for ATP synthesis. Hence, the membrane potential and proton gradient are not equivalent under normal operating conditions far from equilibrium. These conclusions are corroborated by the finding that only the membrane potential induces a rotary torque that drives the counter-rotation of the a and c subunits in the F(o) motor of Propionigenium modestum ATP synthase.




© The Company of Biologists Ltd 2000