Cells of Methanohalophilus halophilus swelled when exposed to hypotonic solutions of NaCl at pH 7.0. The swelling of the cells ceased in the presence of Mg2+. Methane formation by non-growing cells was strongly dependent on the NaCl concentration. Among other monovalent and divalent cations only Li+ and Mg2+ could partly substitute for a specific function of sodium ions. The artificial Na+/H+ antiporter, monensin, exerted a strong inhibitory effect on methane formation from methylamine. The membrane-bound Mg(2+)-stimulated ATPase of these cells was enhanced at low (40 mM) NaCl concentration while higher concentrations of this solute were inhibitory. The results obtained show that sodium ions are a prerequisite for optimal methane formation and ATPase activity in these cells. However, both of these processes required different sodium ion concentrations.

Institute of Animal Biochemistry and Genetics Slovak Academy of Sciences Ivanka pri Dunaji Czechoslovakia

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