Generation of a transmembrane gradient of Na+ in Methanosarcina barkeri

A transmembrane Na+ gradient was generated by Methanosarcina barkeri during methanogenesis. The intracellular Na+ concentration amounted to approximately one fifth of the extracellular one. A secondary Na+/H+ antiport system was shown to be responsible for Na+ extrusion. This system could be inhibited by amiloride. In the presence of amiloride the delta pH across the cytoplasmic membrane increased and a transmembrane Na+ gradient could neither be generated nor maintained. The possible role of Na+ in the oxidation of methanol to the level of formaldehyde is discussed.