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Functional asymmetry of the F 0 motor in bacterial ATP synthases
Author(s) -
Wiedenmann Alexander,
Dimroth Peter,
Von Ballmoos Christoph
Publication year - 2009
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2009.06658.x
Subject(s) - chemiosmosis , atp synthase , electrochemical gradient , biology , atp hydrolysis , biophysics , membrane , adenosine triphosphate , biochemistry , cellular respiration , enzyme , respiratory chain , electron transport chain , membrane potential , respiration , ion transporter , electrochemical potential , mitochondrion , atpase , electrochemistry , chemistry , botany , electrode
Summary F 1 F 0 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 F 0 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 F 0 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.