UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa , 2829-516 Caparica, Portugal.
J Am Chem Soc. 2016 Jul 20;138(28):8834-46. doi: 10.1021/jacs.6b03941. Epub 2016 Jul 7.
Carbon dioxide accumulation is a major concern for the ecosystems, but its abundance and low cost make it an interesting source for the production of chemical feedstocks and fuels. However, the thermodynamic and kinetic stability of the carbon dioxide molecule makes its activation a challenging task. Studying the chemistry used by nature to functionalize carbon dioxide should be helpful for the development of new efficient (bio)catalysts for atmospheric carbon dioxide utilization. In this work, the ability of Desulfovibrio desulfuricans formate dehydrogenase (Dd FDH) to reduce carbon dioxide was kinetically and mechanistically characterized. The Dd FDH is suggested to be purified in an inactive form that has to be activated through a reduction-dependent mechanism. A kinetic model of a hysteretic enzyme is proposed to interpret and predict the progress curves of the Dd FDH-catalyzed reactions (initial lag phase and subsequent faster phase). Once activated, Dd FDH is able to efficiently catalyze, not only the formate oxidation (kcat of 543 s(-1), Km of 57.1 μM), but also the carbon dioxide reduction (kcat of 46.6 s(-1), Km of 15.7 μM), in an overall reaction that is thermodynamically and kinetically reversible. Noteworthy, both Dd FDH-catalyzed formate oxidation and carbon dioxide reduction are completely inactivated by cyanide. Current FDH reaction mechanistic proposals are discussed and a different mechanism is here suggested: formate oxidation and carbon dioxide reduction are proposed to proceed through hydride transfer and the sulfo group of the oxidized and reduced molybdenum center, Mo(6+)═S and Mo(4+)-SH, are suggested to be the direct hydride acceptor and donor, respectively.
二氧化碳积累是生态系统的主要关注点，但由于其丰富的储量和低廉的成本，它成为了生产化学原料和燃料的有趣来源。然而，二氧化碳分子的热力学和动力学稳定性使其活化成为一项具有挑战性的任务。研究自然界用于二氧化碳功能化的化学应该有助于开发新的高效（生物）催化剂，以利用大气中的二氧化碳。在这项工作中，脱硫弧菌(formate dehydrogenase, Dd FDH)还原二氧化碳的能力在动力学和机制上进行了表征。推测 Dd FDH 以非活性形式存在，需要通过依赖还原的机制进行激活。提出了一个滞后酶的动力学模型，以解释和预测 Dd FDH 催化反应的进展曲线（初始滞后阶段和随后的更快阶段）。一旦被激活，Dd FDH 不仅能够有效地催化甲酸盐的氧化（kcat 为 543 s(-1)，Km 为 57.1 μM），还能够催化二氧化碳的还原（kcat 为 46.6 s(-1)，Km 为 15.7 μM），整个反应在热力学和动力学上都是可逆的。值得注意的是，氰化物可完全使 Dd FDH 催化的甲酸盐氧化和二氧化碳还原失活。当前的 FDH 反应机制的提议进行了讨论，并提出了一种不同的机制：甲酸盐氧化和二氧化碳还原被提议通过氢化物转移进行，氧化和还原的钼中心的磺基，Mo(6+)═S 和 Mo(4+)-SH，分别被提议为直接的氢化物受体和供体。
