TAILIEUCHUNG - Báo cáo khoa học: Bioenergetics of the formyl-methanofuran dehydrogenase and heterodisulfide reductase reactions in Methanothermobacter thermautotrophicus

The synthesis of formyl-methanofuran and the reduction of the heterodisulfide (CoM-S-S-CoB) of coenzyme M (HS-CoM) and coenzyme B (HS-CoB) are two crucial, H2 -dependent reactions in the energy metabolism of meth-anogenic archaea. The bioenergetics of the reactionsin vivo were studied in chemostat cultures and in cell suspensions of Methanothermobacter thermautotrophicusmetabolizing at defined dissolved hydrogen partial pressures (pH2 ). | Eur. J. Biochem. 270 66-75 2003 FEBS 2003 doi Bioenergetics of the formyl-methanofuran dehydrogenase and heterodisulfide reductase reactions in Methanothermobacter thermautotrophicus Linda M. I. de Poorter1 Wim G. Geerts1 Alexander P. R. Theuvenet2 and Jan T. Keltjens1 1 Department of Microbiology Faculty of Science and department of Cell Biology Faculty of Science University of Nijmegen the Netherlands The synthesis of formyl-methanofuran and the reduction of the heterodisulfide CoM-S-S-CoB of coenzyme M HS-CoM and coenzyme B HS-CoB are two crucial H2-dependent reactions in the energy metabolism of methanogenic archaea. The bioenergetics of the reactions in vivo were studied in chemostat cultures and in cell suspensions of Methanothermobacter thermautotrophicus metabolizing at defined dissolved hydrogen partial pressures pH . Formyl-methanofuran synthesis is an endergonic reaction AG 16 kJ-mol-1 . By analyzing the concentration ratios between formyl-methanofuran and methanofuran in the cells free energy changes under experimental conditions AG were found to range between 10 and 35 kJ-mol-1 depending on the pH applied. The comparison with the sodium motive force indicated that the reaction should be driven by the import of a variable number of two to four sodium ions. Heterodisulfide reduction AG -40 kJ-mol-1 was associated with free energy changes as high as -55 to -80 kJ-mol-1. The values were determined by analyzing the concentrations of CoM-S-S-CoB HS-CoM and HS-CoB in methane-forming cells operating under a variety of hydrogen partial pressures. Free energy changes were in equilibrium with the proton motive force to the extent that three to four protons could be translocated out of the cells per reaction. Remarkably an apparent proton translocation stoichiometry of three held for cells that had been grown at pH bar whilst the number was four for cells grown above that concentration. The shift occurred within a narrow pi I

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