Proton translocation coupled to methanogenesis from methanol + hydrogen in Methanosarcina barkeri

Addition of methanol to resting cells of Methanosarcina barkeri incubated under an atmosphere of molecular hydrogen resulted in an acidification of the medium. This acidification was not observed when H2 was replaced by N2 or air, or when the uncoupler tetrachlorosalicylanilide was present. 2‐Bromoethanesulfonate completely inhibited both methanogenesis and proton extrusion. N,N′‐Dicyclohexylcarbodiimide, an inhibitor of the proton‐translocating ATPase in M. barkeri, did not affect proton extrusion. Therefore, it could be concluded that proton translocation was coupled to the terminal methylcoenzyme M methylreductase reaction and that it was not due to an H+‐translocating ATPase. A maximum value of 4 H+ translocated per CH4 formed was calculated.