Bioenergetics of the formyl-methanofuran dehydrogenase and heterodisulfide reductase reactions in Methanothermobacter thermautotrophicus
Bioenergetics of the formyl-methanofuran dehydrogenase and heterodisulfide reductase reactions in Methanothermobacter thermautotrophicus
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DOI：
10.1046/j.1432-1033.2003.03362.x
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发表时间：
2003-01-01
期刊：
影响因子：
--
通讯作者：
Keltjens, JT
中科院分区：
文献类型：
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作者：
de Poorter, LMI;Geerts, WG;Keltjens, JT
甲酰甲烷呋喃的合成和辅酶M（HS-CoM）和辅酶B（HS-Co B）的异二硫键（CoM-S-S-Co B）的还原是产甲烷古菌能量代谢中两个重要的H-2依赖性反应。在恒化培养物和在确定的溶解氢分压（p（H2））下代谢的嗜热甲烷热杆菌的细胞悬浮液中研究了体内反应的生物能量学。甲酰基甲烷呋喃合成是一种吸能反应（DeltaGdegrees' = +16 kJ.mol（-1））。通过分析细胞中甲酰基-亚甲基呋喃和亚甲基呋喃之间的浓度比，发现实验条件下的自由能变化（Δ G ′）在+10和+35 kJ·mol（-1）之间，取决于所施加的p（H2）。异二硫键还原（Δ G度' = -40 kJ·mol（-1））的自由能变化高达-55 ~-80 kJ·mol（-1）。通过分析在各种氢分压下操作的甲烷形成电池中CoM-S-S-CoB、HS-CoM和HS-CoB的浓度来确定这些值。自由能的变化与质子动力平衡，以至于每次反应可以有三到四个质子从细胞中转移出来。值得注意的是，在p（H2）< 0.12巴下生长的细胞的表观质子易位化学计量为3，而在高于该浓度下生长的细胞的表观质子易位化学计量为4。该转变发生在约0.12巴的窄p（H2）范围内。研究结果表明，甲烷菌调节生物能源机械参与CoM-S-S-CoB还原和质子泵响应于环境的氢浓度。
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, H-2-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 (p(H2)). Formyl-methanofuran synthesis is an endergonic reaction (DeltaGdegrees' = +16 kJ.mol(-1)). By analyzing the concentration ratios between formyl-methanofuran and methanofuran in the cells, free energy changes under experimental conditions (DeltaG') were found to range between +10 and +35 kJ.mol(-1) depending on the p(H2) 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 (DeltaGdegrees' = -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 p(H2) < 0.12 bar, whilst the number was four for cells grown above that concentration. The shift occurred within a narrow p(H2) span around 0.12 bar. The findings suggest that the methanogens regulate the bioenergetic machinery involved in CoM-S-S-CoB reduction and proton pumping in response to the environmental hydrogen concentrations.