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

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Abstract
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 .