Functional asymmetry of the F0 motor in bacterial ATP synthases |
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Authors: | Alexander Wiedenmann Peter Dimroth Christoph von Ballmoos |
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Institution: | Institut für Mikrobiologie, ETH Zürich, Wolfgang-Pauli-Str. 10, CH-8093 Zürich, Switzerland. |
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Abstract: | F1F0 ATP synthases use the electrochemical potential of H+ or Na+ across biological membranes to synthesize ATP by a rotary mechanism. In bacteria, the enzymes can act in reverse as ATP-driven ion pumps creating the indispensable membrane potential. Here, we demonstrate that the F0 parts of a Na+- and H+-dependent enzyme display major asymmetries with respect to their mode of operation, reflected by the requirement of ~100 times higher Na+ or H+ concentrations for the synthesis compared with the hydrolysis of ATP. A similar asymmetry is observed during ion transport through isolated F0 parts, indicating different affinities for the binding sites in the a/c interface. Together with further data, we propose a model that provides a rationale for a differential usage of membrane potential and ion gradient during ATP synthesis as observed experimentally. The functional asymmetry might also reflect an important property of the ATP synthesis mechanism in vivo . In Escherichia coli , we observed respiratory chain-driven ATP production at pH 7–8, while P -site pH values < 6.5 were required for ATP synthesis in vitro . This discrepancy is discussed with respect to the hypothesis that during respiration lateral proton diffusion could lead to significant acidification at the membrane surface. |
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