title: Carbon monoxide-dependent methyl coenzyme M methylreductase in acetotrophic Methosarcina spp.
abstract: Cell extracts of acetate-grown Methanosarcina strain TM-1 and Methanosarcina acetivorans both contained CH3-S-CoM methylreductase activity. The methylreductase activity was supported by CO and H2 but not by formate as electron donors. The CO-dependent activity was equivalent to the H2-dependent activity in strain TM-1 and was fivefold higher than the H2-dependent activity of M. acetivorans. When strain TM-1 was cultured on methanol, the CO-dependent activity was reduced to 5% of the activity in acetate-grown cells. Methanobacterium formicicum grown on H2-CO2 contained no CO-dependent methylreductase activity. The CO-dependent methylreductase of strain TM-1 had a pH optimum of 5.5 and a temperature optimum of 60 degrees C. The activity was stimulated by the addition of MgCl2 and ATP. Both acetate-grown strain TM-1 and acetate-grown M. acetivorans contained CO dehydrogenase activities of 9.1 and 3.8 U/mg, respectively, when assayed with methyl viologen. The CO dehydrogenase of acetate-grown cells rapidly reduced FMN and FAD, but coenzyme F420 and NADP+ were poor electron acceptors. No formate dehydrogenase was detected in either organism when grown on acetate. The results suggest that a CO-dependent CH3-S-CoM methylreductase system is involved in the pathway of the conversion of acetate to methane and that free formate is not an intermediate in the pathway.
mesh_terms: D000085:Acetates / Q000378:metabolism*; D002248:Carbon Monoxide / Q000494:pharmacology*; D004579:Electron Transport; D019605:Euryarchaeota / Q000201:enzymology* / Q000254:growth & development; D007700:Kinetics; D008697:Methane / Q000378:metabolism; D010088:Oxidoreductases / Q000378:metabolism*; D013045:Species Specificity
chemical_list: D000085:Acetates; D002248:Carbon Monoxide; D010088:Oxidoreductases; C023895:methyl coenzyme M methylreductase; D008697:Methane