Discrimination between transmembrane ion gradient‐driven and electron transfer‐driven ATP synthesis in the methanogenic bacteria

As with Methanococcus voltae [(1986) FEBS Lett. 200, 177–180], ATP synthesis in Methanobacterium thermoautotrophicum (ΔH) can be driven by the imposition of a sodium gradient, but only in the presence of a counterion. Monensin (but not SF6847) inhibits this synthesis. Methanogenic electron transfer‐driven ATP synthesis, however, is insensitive to the combination of these two ionophores. In M. voltae, 117 μM diethylstilbestrol effectively inhibits both membrane potential‐ and sodium gradient‐driven ATP synthesis, but has no effect on ATP production coupled to methanogenesis. In Mb. thermoautotrophicum (ΔH), a similar pattern of inhibition is exhibited by harmaline, an inhibitor of sodium‐linked membrane transport systems. We conclude that ATP‐driven sodium translocation and electron transfer‐driven ATP synthesis are accomplished by separate entities, at least for these two only distantly related species of methanogen.