Oxidation of methane by a biological dicopper centre.
Oxidation of methane by a biological dicopper centre.
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由于缺乏经济和可持续的选择性氧化成甲醇的策略，世界上大量的甲烷气储量作为生产液体燃料和化学品的原料未得到充分利用。目前活化甲烷中强C-H键（104 kcal/mol）的方法需要高温，成本高且效率低，并产生废物。在自然界中，甲烷氧化细菌在环境条件下使用称为甲烷单加氧酶（MMO）的金属酶进行此反应。因此，MMO是高效绿色催化剂的最佳灵感。有两种类型的MMO。可溶性MMO（sMMO），这是表达的几株甲烷氧化菌在铜限制条件下，氧化甲烷具有良好的特征催化二铁中心。颗粒甲烷单加氧酶（pMMO）是由所有甲烷氧化菌产生的一种膜金属酶，由pmoA、pmoB和pmoC三个亚基组成，它们以α3β3γ3三聚体形式排列。尽管有20年的研究和两种晶体结构的可用性，但pMMO金属活性位点的金属组成和位置尚不清楚。在这里，我们表明，pMMO活性是依赖于铜，而不是铁，铜的活性位点位于可溶性结构域的pmoB亚基，而不是在膜内。pmoB的重组可溶性片段（spmoB）结合铜并表现出丙烯和甲烷氧化活性。通过诱变破坏spmoB中的每个铜中心表明活性位点是双铜中心。这些发现解决了pMMO的争议，并为开发环境友好的C-H氧化催化剂提供了一种有前途的新方法。
Vast world reserves of methane gas are underutilized as a feedstock for production of liquid fuels and chemicals due to the lack of economical and sustainable strategies for selective oxidation to methanol. Current processes to activate the strong C–H bond (104 kcal/mol) in methane require high temperatures, are costly and inefficient, and produce waste. In nature, methanotrophic bacteria perform this reaction under ambient conditions using metalloenzymes called methane monooxygenases (MMOs). MMOs are thus the optimal inspiration for an efficient, green catalyst. There are two types of MMOs. Soluble MMO (sMMO), which is expressed by several strains of methanotrophs under copper limited conditions, oxidizes methane with a well characterized catalytic diiron center. Particulate methane monooxygenase (pMMO), an integral membrane metalloenzyme produced by all methanotrophs, is composed of three subunits, pmoA, pmoB, and pmoC, arranged in a trimeric α3β3γ3 complex. Despite 20 years of research and the availability of two crystal structures, the metal composition and location of the pMMO metal active site are not known. Here we show that pMMO activity is dependent on copper, not iron, and that the copper active site is located in the soluble domains of the pmoB subunit rather than within the membrane. Recombinant soluble fragments of pmoB (spmoB) bind copper and exhibit propylene and methane oxidation activities. Disruption of each copper center in spmoB by mutagenesis indicates that the active site is a dicopper center. These findings resolve the pMMO controversy and provide a promising new approach to developing environmentally friendly C–H oxidation catalysts.
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