Laboratory of Organic Chemistry, ETH Zurich, Wolfgang-Pauli-Str. 10, 8093 Zurich, Switzerland.
Nature. 2010 Jun 3;465(7298):606-8. doi: 10.1038/nature09015.
Large amounts (estimates range from 70 Tg per year to 300 Tg per year) of the potent greenhouse gas methane are oxidized to carbon dioxide in marine sediments by communities of methanotrophic archaea and sulphate-reducing bacteria, and thus are prevented from escaping into the atmosphere. Indirect evidence indicates that the anaerobic oxidation of methane might proceed as the reverse of archaeal methanogenesis from carbon dioxide with the nickel-containing methyl-coenzyme M reductase (MCR) as the methane-activating enzyme. However, experiments showing that MCR can catalyse the endergonic back reaction have been lacking. Here we report that purified MCR from Methanothermobacter marburgensis converts methane into methyl-coenzyme M under equilibrium conditions with apparent V(max) (maximum rate) and K(m) (Michaelis constant) values consistent with the observed in vivo kinetics of the anaerobic oxidation of methane with sulphate. This result supports the hypothesis of 'reverse methanogenesis' and is paramount to understanding the still-unknown mechanism of the last step of methanogenesis. The ability of MCR to cleave the particularly strong C-H bond of methane without the involvement of highly reactive oxygen-derived intermediates is directly relevant to catalytic C-H activation, currently an area of great interest in chemistry.
大量（估计每年 70 到 300 公吨）的强温室气体甲烷在海洋沉积物中被产甲烷古菌和硫酸盐还原菌组成的群落氧化为二氧化碳，从而防止其逸入大气。间接证据表明，甲烷的厌氧氧化可能是通过含镍的甲基辅酶 M 还原酶（MCR）作为甲烷激活酶，从二氧化碳逆反应进行的古菌甲烷生成。然而，缺乏证明 MCR 可以催化吸能反向反应的实验。在这里，我们报告来自 Methanothermobacter marburgensis 的纯化 MCR 在平衡条件下将甲烷转化为甲基辅酶 M，其表观 V(max)（最大速率）和 K(m)（米氏常数）值与硫酸盐存在时甲烷厌氧氧化的体内动力学一致。这一结果支持“反向甲烷生成”假说，对于理解甲烷生成最后一步的未知机制至关重要。MCR 能够在不涉及高反应性氧衍生中间体的情况下裂解甲烷特别强的 C-H 键，这与目前化学领域非常关注的催化 C-H 活化直接相关。
