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Journal of Bacteriology, April 2002, p. 1947-1951, Vol. 184, No. 7
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.7.1947-1951.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Chemiosmotic Energy Conservation with Na⁺ as the Coupling Ion during Hydrogen-Dependent Caffeate Reduction by Acetobacterium woodii

Lehrstuhl für Mikrobiologie der Ludwig-Maximilians-Universität München, D-80638 Munich, Germany

Received 28 September 2001/ Accepted 9 January 2002

Cell suspensions of Acetobacterium woodii prepared from cultures grown on fructose plus caffeate catalyzed caffeate reduction with electrons derived from molecular hydrogen. Hydrogen-dependent caffeate reduction was strictly Na⁺ dependent with a K_m for Na⁺ of 0.38 mM; Li⁺ could substitute for Na⁺. The sodium ionophore ETH2120, but not protonophores, stimulated hydrogen-dependent caffeate reduction by 280%, indicating that caffeate reduction is coupled to the buildup of a membrane potential generated by primary Na⁺ extrusion. Caffeate reduction was coupled to the synthesis of ATP, and again, ATP synthesis coupled to hydrogen-dependent caffeate reduction was strictly Na⁺ dependent and abolished by ETH2120, but not by protonophores, indicating the involvement of a transmembrane Na⁺ gradient in ATP synthesis. The ATPase inhibitor N,N'-dicyclohexylcarbodiimide (DCCD) abolished ATP synthesis, and at the same time, hydrogen-dependent caffeate reduction was inhibited. This inhibition could be relieved by ETH2120. These experiments are fully compatible with a chemiosmotic mechanism of ATP synthesis with Na⁺ as the coupling ion during hydrogen-dependent caffeate reduction by A. woodii.

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