Department of Molecular Biology and Biochemistry, University of California, Irvine, CA, 92697-3900, USA.
Department of Chemistry, University of California, Irvine, CA, 92697-2025, USA.
Chemistry. 2019 Feb 18;25(10):2389-2395. doi: 10.1002/chem.201803735. Epub 2018 Dec 6.
Nitrogenase utilizes an ATP-dependent reductase to deliver electrons to its catalytic component to enable two important reactions: the reduction of N to NH , and the reduction of CO to hydrocarbons. The two nitrogenase-based reactions parallel the industrial Haber-Bosch and Fischer-Tropsch processes, yet they occur under ambient conditions. As such, understanding the enzymatic mechanism of nitrogenase is crucial for the future development of biomimetic strategies for energy-efficient production of valuable chemical commodities. Mechanistic investigations of nitrogenase has long been hampered by the difficulty to trap substrates and intermediates relevant to the nitrogenase reactions. Recently, we have successfully captured CO on the Azotobacter vinelandii V-nitrogenase via two approaches that alter the electron fluxes in a controlled manner: one approach utilizes an artificial electron donor to trap CO on the catalytic component of V-nitrogenase in the resting state; whereas the other employs a mismatched reductase component to reduce the electron flux through the system and consequently accumulate CO on the catalytic component of V-nitrogenase. Here we summarize the major outcome of these recent studies, which not only clarified the catalytic relevance of the one-CO (lo-CO) and multi-CO (hi-CO) bound states of nitrogenase, but also pointed to a potential competition between N and CO for binding to the same pair of reactive Fe sites across the sulfur belt of the cofactor. Together, these results highlight the utility of these strategies in poising the cofactor at a well-defined state for substrate- or intermediate-trapping via controlled alteration of electron fluxes, which could prove beneficial for further elucidation of the mechanistic details of nitrogenase-catalyzed reactions.
固氮酶利用 ATP 依赖型还原酶将电子传递给其催化组件，以实现两个重要反应：将 N 还原为 NH 3 ，以及将 CO 还原为碳氢化合物。这两个基于固氮酶的反应与工业 Haber-Bosch 和 Fischer-Tropsch 过程平行，但它们在环境条件下发生。因此，了解固氮酶的酶促机制对于未来开发节能生产有价值化学商品的仿生策略至关重要。固氮酶的机制研究长期以来一直受到难以捕获与固氮酶反应相关的底物和中间体的阻碍。最近，我们通过两种方法成功地在 Azotobacter vinelandii V 型固氮酶上捕获了 CO，这两种方法以受控的方式改变电子通量：一种方法利用人工电子供体在 V 型固氮酶的催化组件的静止状态下捕获 CO；而另一种方法则利用不匹配的还原酶组件来降低电子通量通过系统，并因此在 V 型固氮酶的催化组件上积累 CO。在这里，我们总结了这些最近研究的主要结果，这些结果不仅阐明了固氮酶的单 CO（lo-CO）和多 CO（hi-CO）结合态的催化相关性，而且还指出了 N 和 CO 之间可能存在竞争，以结合到同一对反应性 Fe 位点上，跨越辅因子的硫带。总之，这些结果强调了这些策略在通过控制电子通量的改变将辅因子置于定义明确的状态下用于底物或中间体捕获的实用性，这可能有助于进一步阐明固氮酶催化反应的机制细节。
