Evolution of Na⁺ and H⁺ bioenergetics in methanogenic archaea

Methanogenic archaea live at the thermodynamic limit of life and use sophisticated mechanisms for ATP synthesis and energy coupling. The group of methanogens without cytochromes use an Na⁺ current across the membrane for ATP synthesis, whereas the cytochrome-containing methanogens have additional coupling sites that also translocate protons. The ATP synthase in this group is promiscuous and uses Na⁺ and H⁺ simultaneously.