title: Temperature dependence of methyl-coenzyme M reductase activity and of the formation of the methyl-coenzyme M reductase red2 state induced by coenzyme B.
abstract: Methyl-coenzyme M reductase (MCR) catalyses the formation of methane from methyl-coenzyme M (CH(3)-S-CoM) and coenzyme B (HS-CoB) in methanogenic archaea. The enzyme has an alpha(2)beta(2)gamma(2) subunit structure forming two structurally interlinked active sites each with a molecule F(430) as a prosthetic group. The nickel porphinoid must be in the Ni(I) oxidation state for the enzyme to be active. The active enzyme exhibits an axial Ni(I)-based electron paramagnetic resonance (EPR) signal and a UV-vis spectrum with an absorption maximum at 385 nm. This state is called the MCR-red1 state. In the presence of coenzyme M (HS-CoM) and coenzyme B the MCR-red1 state is in part converted reversibly into the MCR-red2 state, which shows a rhombic Ni(I)-based EPR signal and a UV-vis spectrum with an absorption maximum at 420 nm. We report here for MCR from Methanothermobacter marburgensis that the MCR-red2 state is also induced by several coenzyme B analogues and that the degree of induction by coenzyme B is temperature-dependent. When the temperature was lowered below 20 degrees C the percentage of MCR in the red2 state decreased and that in the red1 state increased. These changes with temperature were fully reversible. It was found that at most 50% of the enzyme was converted to the MCR-red2 state under all experimental conditions. These findings indicate that in the presence of both coenzyme M and coenzyme B only one of the two active sites of MCR can be in the red2 state (half-of-the-sites reactivity). On the basis of this interpretation a two-stroke engine mechanism for MCR is proposed.
authors.affiliation: Max-Planck-Institut für terrestrische Mikrobiologie and Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, Karl-von-Frisch-Strasse, 35043 Marburg, Germany.
authors.forename: Meike
authors.initials: M
authors.lastname: Goenrich
authors.forename: Evert C
authors.initials: EC
authors.lastname: Duin
authors.forename: Felix
authors.initials: F
authors.lastname: Mahlert
authors.forename: Rudolf K
authors.initials: RK
authors.lastname: Thauer
mesh_terms: D001665:Binding Sites; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D015080:Mesna / Q000031:analogs & derivatives; D017013:Methanobacteriaceae / Q000201:enzymology* / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D010769:Phosphothreonine / Q000031:analogs & derivatives* / Q000378:metabolism; D013696:Temperature
chemical_list: C049349:7-mercaptoheptanoylthreonine phosphate; D010769:Phosphothreonine; C023349:methyl coenzyme M; D010088:Oxidoreductases; C021572:methyl coenzyme M reductase; D015080:Mesna