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

Abstract

The addition of methanol to a cell suspension of M. 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 > 90% of the membrane potential .DELTA..psi.. These values were similar under N2 and H2. The addition of the uncoupler tetrachlorosalicylanilide to the above system under N2 led to a drastic decrease of the ATP concentration and the .DELTA.p and to a stop of methanogenesis. With methanol and H2, CH4 formation continued, although the effect of the uncoupler on the ATP pool and on .DELTA.p was the same as under N2. The proton-translocating ATPase inhibitor N,N''-dicyclohexylcarbodiimide caused a rapid exhaustion of the ATP pool and a discontinuation of CH4 synthesis, whereas .DELTA.p was unaffected. Inhibition of CH4 formation under these conditions could be relieved by the addition of the uncoupler tetrachlorosalicylanilide. Apparently CH4 formation according to the equation CH3OH + H2 .fwdarw. CH4 + H2O was coupled to ATP synthesis by a chemiosmotic mechanism and was under the control of .DELTA..psi.. CH4 formation only proceeded if the .DELTA..psi. generated was used for ATP synthesis or if an uncoupler was present. Under N2, CH4 formation according to the equation 4 CH3OH .fwdarw. CO2 + 3 CH4 + 2H2O was abolished by an uncoupler, because 1 step in the oxidation of methanol to 1CO2 apparently depended on an energized state of the membrane.