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Charge Displacements during ATP-Hydrolysis and Synthesis of the Na⁺-Transporting F_oF₁-ATPase of Ilyobacter tartaricus

Christiane Burzik ^*, Georg Kaim , Peter Dimroth , Ernst Bamberg ^*  and Klaus Fendler ^*

^* Max-Planck-Institut für Biophysik, D-60596 Frankfurt/Main, Germany; Eidgenössische Technische Hochschule Zürich, CH-8092 Zürich, Switzerland; and Universität Frankfurt, D-60439 Frankfurt-Main, Germany

Correspondence: Address reprint requests to Klaus Fendler, Marie Curie Str. 15, Frankfurt/Main, Germany D-60439. Tel.: 49-69-6303-2035; Fax: 49-69-6303-2002; E-mail: klaus.fendler{at}mpibp-frankfurt.mpg.de.

Transient electrical currents generated by the Na⁺-transporting F_oF₁-ATPase of Ilyobacter tartaricus were observed in the hydrolytic and synthetic mode of the enzyme. Two techniques were applied: a photochemical ATP concentration jump on a planar lipid membrane and a rapid solution exchange on a solid supported membrane. We have identified an electrogenic reaction in the reaction cycle of the F_oF₁-ATPase that is related to the translocation of the cation through the membrane bound F_o subcomplex of the ATPase. In addition, we have determined rate constants for the process: For ATP hydrolysis this reaction has a rate constant of 15–30 s^-1 if H⁺ is transported and 30–60 s^-1 if Na⁺ is transported. For ATP synthesis the rate constant is 50–70 s^-1.

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