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Please use this identifier to cite or link to this item: http://ir.ncue.edu.tw/ir/handle/987654321/15142

Title: Mechanistic Studies of Methane Biogenesis by Methyl-Coenzyme M Reductase: Evidence that Coenzyme B Participates in Cleaving the C-S Bond of Methyl-Coenzyme M
Authors: Horng, Yih-Chern;Becker, Donald F.;Ragsdale, Stephen W.
Contributors: 化學系
Date: 2001-10
Issue Date: 2013-01-07T02:15:46Z
Publisher: American Chemical Society
Abstract: Methyl-coenzyme M reductase (MCR), the key enzyme in methanogenesis, catalyzes methane formation from methyl-coenzyme M (methyl-SCoM) and N-7-mercaptoheptanoylthreonine phosphate (CoBSH). Steady-state and presteady-state kinetics have been used to test two mechanistic models that contrast in the role of CoBSH in the MCR-catalyzed reaction. In class 1 mechanisms, CoBSH is integrally involved in methane formation and in C-S (methyl-SCoM) bond cleavage. On the other hand, in class 2 mechanisms, methane is formed in the absence of CoBSH, which functions to regenerate active MCR after methane is released. Steady-state kinetic studies are most consistent with a ternary complex mechanism in which CoBSH binds before methane is formed, as found earlier [Bonacker et al. (1993) Eur. J. Biochem. 217, 587-595]. Presteady-state kinetic experiments at high MCR concentrations are complicated by the presence of tightly bound CoBSH in the purified enzyme. Chemical quench studies in which (14)CH(3)-SCoM is rapidly reacted with active MCRred1 in the presence versus the absence of added CoBSH indicate that CoBSH is required for a single-turnover of methyl-SCoM to methane. Similar single turnover studies using a CoBSH analogue leads to the same conclusion. The results are consistent with class 1 mechanisms in which CoBSH is integrally involved in methane formation and in C-S (methyl-SCoM) bond cleavage and are inconsistent with class 2 mechanisms in which CoBSH binds after methane is formed. These are the first reported pre-steady-state kinetic studies of MCR.
Relation: Biochemistry, 40(43): 12875-12885
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