Component of the methyl-coenzyme M reductase (MCR) I that catalyzes the reductive cleavage of methyl-coenzyme M (CoM-S-CH3 or 2-(methylthio)ethanesulfonate) using coenzyme B (CoB or 7-mercaptoheptanoylthreonine phosphate) as reductant which results in the production of methane and the mixed heterodisulfide of CoB and CoM (CoM-S-S-CoB). This is the final step in methanogenesis (PubMed:2269306, PubMed:3350018). Neither N-6-mercaptohexanoylthreonine phosphate (H-S-HxoTP) nor N-8-mercaptooctanoylthreonine phosphate (H-SOcoTP) nor any other thiol compound such as CoA or CoM can substitute for CoB as the electron donor (PubMed:3350018). coenzyme B + methyl-coenzyme M = coenzyme M-coenzyme B heterodisulfide + methane Binds 2 coenzyme F430 non-covalently per MCR complex. Coenzyme F430 is a yellow nickel porphinoid (PubMed:3350018, PubMed:9367957). Methyl-coenzyme-M reductase is activated when the enzyme-bound coenzyme F430 is reduced to the Ni(I) oxidation state (PubMed:9030728). Methyl-coenzyme M reductase activity is inhibited by 3-nitrooxypropanol (3-NOP) in vitro and in vivo, by oxidation of its active site Ni(I), which stops both growth and methanogenesis (PubMed:27140643). Is also inhibited by the reaction product CoM-S-S-CoB (PubMed:3350018). One-carbon metabolism; methyl-coenzyme M reduction; methane from methyl-coenzyme M: step 1/1. MCR is a hexamer of two alpha, two beta, and two gamma chains, forming a dimer of heterotrimers. Under growth limiting conditions on nickel-depleted media, a fraction of 70% of the enzyme is localized close to the cytoplasmic membrane, which implies 'facultative' membrane association of the enzyme. There are two MCR complexes in this bacteria. MCR II is expressed in the early growth phase. Late growth cells contain mostly MCR I. The MCR reaction has been shown to follow an ordered bi-bi ternary complex mechanism, in which methyl-SCoM must enter the MCR active site prior to CoB for a productive catalysis. Belongs to the methyl-coenzyme M reductase beta subunit family.