Open AccessProton‐motive‐force‐driven formation of CO from CO 2 and H 2 in methanogenic bacteria
Author(s) -
BOTT Michael,
THAUER Rudolf K.
Publication year - 1987
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1987.tb13434.x
Subject(s) - protonophore , methanogenesis , methanobacterium , methanosarcina barkeri , chemiosmosis , chemistry , exergonic reaction , proton , methanomicrobiales , bacteria , intracellular , medicinal chemistry , stereochemistry , atp synthase , biochemistry , membrane potential , methanosarcina , methane , biology , archaea , catalysis , organic chemistry , enzyme , physics , genetics , quantum mechanics , gene
Cell suspensions of methanogenic bacteria ( Methanosarcina barkeri, Methanospirillum hungatei, Methanobrevibacter arboriphilus , and Methanobacterium thermoautotrophicum ) were found to form CO from CO 2 and H 2 according to the reaction: CO 2 + H 2 → CO + H 2 O; ΔG 0 =+20 kJ/mol. Up to 15000 ppm CO in the gas phase were reached which is significantly higher than the equilibrium concentration calculated from ΔG 0 (95 ppm under the experimental conditions). This indicated that CO 2 reduction with H 2 to CO is energy‐driven and indeed the cells only generated CO when forming CH 4 . The coupling of the two reactions was studied in more detail with acetate‐grown cells of M. barkeri using methanol and H 2 as methanogenic substrates. The effects of the protonophore tetrachlorosalicylanilide (TCS) and of the proton‐translocating ATPase inhibitor N,N′ ‐dicyclohexylcarbodiimide (cHxN) 2 C were determined. TCS completely inhibited CO formation from CO 2 and H 2 without affecting methanogenesis from CH 3 OH and H 2 . In the presence of the protonophore the proton motive force Δ p and the intracellular ATP concentration were very low. (cHxN) 2 C, which partially inhibited methanogenesis from CH 3 OH and H 2 , had no effect on CO 2 reduction to CO. In the presence of (cHxN) 2 C Δ p was high and the intracellular ATP content was low. These findings suggest that the endergonic formation of CO from CO 2 and H 2 is coupled to the exergonic formation of CH 4 from CH 3 OH and H 2 via the proton motive force and not via ATP. CO formation was not stimulated by the addition of sodium ions.