The final step in methane formation. Investigations with highly purified methyl-CoM reductase (component C) from Methanobacterium thermoautotrophicum (strain Marburg).
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 mumol 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 microM) and H-S-OcoTP (apparent Ki = 15 microM) were found to be effective inhibitors of methyl-CoM reductase, inhibition being non-competitive with CH3-S-CoM and competitive with H-S-HTP.
Ellermann
J
J
Fachbereich Biologie, Mikrobiologie, Philipps-Universität Marburg, Federal Republic of Germany.
Hedderich
R
R
Böcher
R
R
Thauer
R K
RK
D004220:Disulfides / Q000096:biosynthesis; D019605:Euryarchaeota / Q000201:enzymology / Q000378:metabolism*; D008697:Methane / Q000096:biosynthesis*; D010084:Oxidation-Reduction / Q000187:drug effects; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000494:pharmacology
D004220:Disulfides; D013438:Sulfhydryl Compounds; D010088:Oxidoreductases; C021572:methyl coenzyme M reductase; D008697:Methane