Open AccessCoupling of carbon monoxide oxidation to CO 2 and H 2 with the phosphorylation of ADP in acetate‐grown Methanosarcina barkeri
Author(s) -
BOTT Michael,
EIKMANNS Bernhard,
THAUER Rudolf K.
Publication year - 1986
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1986.tb09881.x
Subject(s) - methanosarcina barkeri , carbon monoxide , carbon monoxide dehydrogenase , methanomicrobiales , chemistry , chemiosmosis , protonophore , atp synthase , medicinal chemistry , inorganic chemistry , methanogenesis , biochemistry , nuclear chemistry , methanosarcina , methane , catalysis , organic chemistry , enzyme , membrane
Cell suspensions of Methanosarcina barkeri , grown on acetate, catalyzed the conversion of carbon monoxide and H 2 O to CO 2 and H 2 in stoichiometric amounts when methane formation was inhibited by bromoethanesulfonate. The specific activity was 80–120 nmol min −1 mg protein −1 at 5% CO in the gas phase. CO oxidation was coupled with the phosphorylation of ADP as indicated by a rapid increase of the intracellular ATP level upon start of the reaction. At least 0.1 mol ATP was formed/mol CO consumed. The onset of CO oxidation was also accompanied by an increase of the proton motive force (Δ p ) from 100 mV to 150 mV (inside negative). Addition of the uncoupler tetrachlorosalicylanilide to CO‐metabolizing cells led to a rapid decrease of the ATP level and of Δ p , and to an increase of the CO oxidation rate up to 70%. In the presence of the proton‐translocating ATPase inhibitor N , N ′‐dicyclohexylcarbodiimide the phosphorylation of ADP was inhibited and CO oxidation slowed down, whereas Δ p was almost unaffected. Inhibition of CO oxidation under these conditions was relieved by the addition of the protonophore tetrachlorosalicylanilide. The results indicate that in acetate‐grown M. barkeri the free‐energy change associated with the formation of CO 2 and H 2 from CO and H 2 O (Δ G °=–20 kJ/mol) can be used to drive the phosphorylation of ADP and that the coupling proceeds via a chemiosmotic mechanism. A possible role of the carbon monoxide oxidation reaction as an energy‐conserving site in acetate fermentation to CH 4 and CO 2 is discussed.