Energiestoffwechsel von Cytochrom-freien methanogenen Archaea bei Wachstum auf H2 und CO2

Methanogene Archaea sind Organismen, die Methan als Endprodukt ihres anaeroben Energiestoffwechsels bilden. Es gibt zwei stoffwechselphysiologisch unterschiedliche Gruppen: Zum einen die Cytochrom-freien Methanogenen, welche nur H2 und CO2 und/oder Formiat zu Methan umsetzen und zum anderen die Cyto...

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Bibliographic Details
Main Author: Kaster, Anne-Kristin
Contributors: Thauer, Rudolf Kurt (Prof.) (Thesis advisor)
Format: Dissertation
Published: Philipps-Universität Marburg 2011
Online Access:PDF Full Text
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Table of Contents: In methanogenic archaea growing on H2 and CO2 the first step in methanogenesis is the endergonic reduction of ferredoxin (Fd) with H2 and the last step is the exergonic reduction of the heterodisulfide CoM-S-S-CoB with H2 to coenzyme M (CoM-SH) and coenzyme B (CoB-SH). We recently proposed that in hydrogenotrophic methanogens the two reactions are energetically coupled via the cytoplasmic MvhADG/HdrABC complex. It is reported here that the purified complex from Methanothermobacter marburgensis catalyzes the CoM-S-S-CoB dependent reduction of Fd with H2. Per mol CoM-S-S-CoB added, which appeared to be completely reduced to CoM-S-H and CoB-SH, one mol of Fd was reduced indicating an electron bifurcation coupling mechanism: 2 H2 + Fdox + CoM-S-S-CoB → Fdred2- + CoM-SH + CoB-SH + 2 H+. This stoichiometry of coupling is consistent with an ATP gain per mol methane from 4 H2 and CO2 of near 0.5 deduced from a H2-threshold concentration of 8 Pa and a growth yield of up to 3 g per mol methane which we have determined for two hydrogenotrophic methanogens.