The final step in methane formation

Abstract

Methyl‐coenzyme M reductase (= component C) from Methanobacterium thermoautotrophicum (strain Marburg) was highly purified via anaerobic fast protein liquid chromatography on columns of Mono Q and Superose 6. The enzyme was found to catalyze the reduction of methylcoenzyme M (CH3‐S‐CoM) with N‐7‐mercaptoheptanoylthreonine phosphate (H‐S‐HTP = component B) to CH4. The mixed disulfide of H‐S‐CoM and H‐S‐HTP (CoM‐S‐S‐HTP) was the other major product formed. The specific activity was up to 75 nmol min−1 mg protein−1. In the presence of dithiothreitol and of reduced corrinoids or titanium(III) citrate the specific rate of CH3‐S‐CoM reduction to CH4 with H‐S‐HTP increased to 0.5–2 μmol min−1 mg protein−1. Under these conditions the CoM‐S‐S‐HTP formed from CH3‐S‐CoM and H‐S‐HTP was completely reduced to H‐S‐CoM and H‐S‐HTP. Methyl‐CoM reductase was specific for H‐S‐HTP as electron donor. Neither N‐6‐mercaptohexanoylthreonine phosphate (H‐S‐HxoTP) nor N‐8‐mercaptooctanoylthreonine phosphate (H‐S‐OcoTP) nor any other thiol compound could substitute for H‐S‐HTP. On the contrary, H‐S‐HxoTP (apparent Ki=0.1 μM) and H‐S‐OcoTP (apparent Ki= 15 μM) were found to be effectives inhibitors of methyl‐CoM reductase, inhibition being non‐competitive with CH3‐S‐CoM and competitive with H‐S‐HTP.

Abiotic methanogenesis from organosulphur compounds under ambient conditions

“…This important consideration is in agreement with previous results that showed enhanced CH 4 formation in animal cells under reduced oxygen content 3,4 . Finally, we suggest that the CH 4 pathway described herein might be considered as an 'oxidative counterpart' of the final step of biological CH 4 formation in methanogenic archaea where the methyl coenzyme M reductase catalyses the reaction between thioether methyl coenzyme M and the thiol N-(7-mercaptoheptanoyl)threonine 3-O-phosphate to give CH 4 and the mixed disulphide 51 .…”

Coupling of ferredoxin and heterodisulfide reduction via electron bifurcation in hydrogenotrophic methanogenic archaea

“…CoM-SH (2-mercaptoethanesulfonate) was from Sigma-Aldrich. CoB-SH, CoB-S-S-CoB, and CoM-S-S-CoM were synthesized as described previously (40). CoM-S-S-CoB was separated from CoM-S-S-CoM and CoM-SH on SERDOLIT PAD II material (0.1-0.2 mm) from Serva.…”

H2: heterodisulfide oxidoreductase complex from Methanobacterium thermoautotrophicum

“…Formylmethanofuran was prepared from methanofuran and p-nitrophenylformate (Donnelly and Wolfe, 1986). CoM-S-S-HTP and its analogues were synthesized as described by Ellermann et al (1988) and Hedderich et al (1990). M. thermoautotrophicum (strain Marburg, DSM 2133) was from the Deutsche Sammlung von Mikroorganismen (Braunschweig, Germany).…”

“…thermoautotrophicum contains high concentrations of a corrinoid protein (Schulz and Fuchs, 1986) and corrinoids are known to catalyze the reduction of disulfides albeit without specificity (Hedderich and Thauer, 1988). We therefore tested whether in the presence of the membrane component, disulfides other than CoM-S-S-HTP were reduced.…”

“…Cell extracts of M. thermoautotrophicurn were shown to catalyze the reduction of CoM-S-S-HTP with H, (H,:heterodisulfide oxidoreductase activity; Hedderich and Thauer, 1988) and with reduced viologen dyes as artificial electron donors (heterodisulfide-reductase activity; Hedderich et al, 1989). Both activities were associated with the soluble cell fraction.…”