Chemiosmotic energy conservation with Na+ as the coupling ion during hydrogen-dependent caffeate reduction by Acetobacterium woodii

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.