Spencer R W, Daniels L, Fulton G, Orme-Johnson W H
Biochemistry. 1980 Aug 5;19(16):3678-83. doi: 10.1021/bi00557a007.
The hydrogen in methane produced by cultures of Methanobacterium thermoautotrophicum originates from water. In H2O/D2O mixtures, a methane product isotope effect is observed that increases rapidly as the water deuterium enrichment approaches 100%. This effect is due to the intracellular production of protons from H2, catalyzed by hydrogenase, which occurs at 12% the rate of water diffusion through the cell membrane. We estimate that water diffusion through the thick cell membrane of M. thermoautotrophicum is retarded by a factor of 10(6) over the free diffusion rate. The intracellular production of H+ suggests that either (1) hydrogenase is not directly involved in the production of a chemiosmotic proton gradient or (2) if it is involved, the proton gradient exists between the cytosol and the interior of vesicles observed in this bacterium. The intrinsic deutrium product isotope effect in methanogenesis is 1.20 +/- 0.1, comparable to anabolic deuterium product isotope effects in other autotrophs. An algebraic model incorporating the intracellular H2 to H+ flux accurately predicts the distribution of deuterated methane species at all levels of water deuterium enrichment.
嗜热自养甲烷杆菌培养物产生的甲烷中的氢源自水。在H₂O/D₂O混合物中，观察到甲烷产物同位素效应，随着水中氘富集度接近100%，该效应迅速增加。这种效应是由于氢化酶催化从H₂产生质子的细胞内过程，其发生速率是水通过细胞膜扩散速率的12%。我们估计，水通过嗜热自养甲烷杆菌厚细胞膜的扩散比自由扩散速率慢10⁶倍。细胞内H⁺的产生表明，要么（1）氢化酶不直接参与化学渗透质子梯度的产生，要么（2）如果它参与其中，质子梯度存在于该细菌中观察到的胞质溶胶和囊泡内部之间。甲烷生成中的固有氘产物同位素效应为1.20±0.1，与其他自养生物中的合成代谢氘产物同位素效应相当。一个包含细胞内H₂到H⁺通量的代数模型准确预测了在所有水氘富集水平下氘化甲烷物种的分布。
