Departments of Molecular Biosciences and of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
J Am Chem Soc. 2016 Aug 3;138(30):9327-40. doi: 10.1021/jacs.6b04568. Epub 2016 Jul 19.
Biological conversion of natural gas to liquids (Bio-GTL) represents an immense economic opportunity. In nature, aerobic methanotrophic bacteria and anaerobic archaea are able to selectively oxidize methane using methane monooxygenase (MMO) and methyl coenzyme M reductase (MCR) enzymes. Although significant progress has been made toward genetically manipulating these organisms for biotechnological applications, the enzymes themselves are slow, complex, and not recombinantly tractable in traditional industrial hosts. With turnover numbers of 0.16-13 s(-1), these enzymes pose a considerable upstream problem in the biological production of fuels or chemicals from methane. Methane oxidation enzymes will need to be engineered to be faster to enable high volumetric productivities; however, efforts to do so and to engineer simpler enzymes have been minimally successful. Moreover, known methane-oxidizing enzymes have different expression levels, carbon and energy efficiencies, require auxiliary systems for biosynthesis and function, and vary considerably in terms of complexity and reductant requirements. The pros and cons of using each methane-oxidizing enzyme for Bio-GTL are considered in detail. The future for these enzymes is bright, but a renewed focus on studying them will be critical to the successful development of biological processes that utilize methane as a feedstock.
天然气制液体燃料（Bio-GTL）具有巨大的经济机遇。在自然界中，好氧甲烷营养菌和厌氧古菌能够利用甲烷单加氧酶（MMO）和甲基辅酶 M 还原酶（MCR）酶选择性地氧化甲烷。尽管在遗传操纵这些生物体以用于生物技术应用方面已经取得了重大进展，但这些酶本身反应缓慢、复杂，并且在传统的工业宿主中不易进行重组。这些酶的周转率为 0.16-13 s(-1)，这在利用甲烷生产燃料或化学品的生物生产中构成了相当大的上游问题。需要对甲烷氧化酶进行工程改造以提高反应速度，从而实现高容积产率；然而，为此进行的努力以及构建更简单的酶的尝试都收效甚微。此外，已知的甲烷氧化酶的表达水平、碳和能量效率、生物合成和功能所需的辅助系统各不相同，在复杂性和还原剂需求方面也有很大差异。详细考虑了每种甲烷氧化酶在 Bio-GTL 中的优缺点。这些酶的前景一片光明，但需要重新关注对它们的研究，这对于成功开发利用甲烷作为原料的生物过程至关重要。
