Coupling of ATP synthesis and methane formation from methanol and molecular hydrogen in Methanosarcina barkeri

The addition of methanol to a cell suspension of Methanosarcina barkeri resulted in an increase of the intracellular ATP concentration from 1 nmol/mg to 10 nmol/mg protein and in the formation of a proton-motive force delta p of -130 mV. delta p consisted of more than 90% of the membrane potential delta psi. These values were similar under N2 and under H2. The addition of the uncoupler tetrachlorosalicylanilide to the above system under N2 led to a drastic decrease of both, the ATP concentration and the delta p and to a stop of methanogenesis. With methanol and H2, however, methane formation continued, although the effect of the uncoupler on the ATP pool and on delta p was a under N2. The proton-translocating ATPase inhibitor N,N'-dicyclohexylcarbodiimide caused a rapid exhaustion of the ATP pool and a discontinuation of methane synthesis, whereas delta p was unaffected. Inhibition of methane formation under these conditions could be relieved by the addition of the uncoupler tetrachlorosalicylanilide. These results demonstrate that methane formation according to the equation CH3OH + H2----H2----CH4 + H2O was coupled to ATP synthesis by a chemiosmotic mechanism and was under the control of delta psi: Methane formation only proceeded if the delta psi generated was used for ATP synthesis or if an uncoupler was present. Under N2, methane formation according to the equation 4CH3OH ----CO2 + 3CH4 + 2H2O was abolished by an uncoupler, because one step in the oxidation of methanol to 1 CO2 apparently depended on an energized state of the membrane.