Abstract：
[NiFe] hydrogenases catalyze the reversible cleavage of molecular hydrogen into protons and electrons. Here, we have studied the impact of temperature and illumination on an oxygen-tolerant and thermostable [NiFe] hydrogenase by IR and EPR spectroscopy. Equilibrium mixtures of two catalytic [NiFe] states, Nia-C and Nia-SR\'\', were found to drastically change with temperature, indicating a thermal exchange of electrons between the [NiFe] active site and iron-sulfur clusters of the enzyme. In addition, IR and EPR experiments performed under illumination revealed an unusual photochemical response of the enzyme. Nia-SR\'\', a fully reduced hydride intermediate of the catalytic cycle, was found to be reversibly photoconverted into another catalytic state, Nia-L. In contrast to the well-known photolysis of the more oxidized hydride intermediate Nia-C, photoconversion of Nia-SR\'\' into Nia-L is an active-site redox reaction that involves light-driven electron transfer towards the enzyme\'s iron-sulfur clusters. Omitting the ground-state intermediate Nia-C, this direct interconversion of these two states represents a potential photochemical shortcut of the catalytic cycle that integrates multiple redox sites of the enzyme. In total, our findings reveal the non-local redistribution of electrons via thermal and photochemical reaction channels and the potential of accelerating or controlling [NiFe] hydrogenases by light.
摘要：
[NiFe]氢化酶催化分子氢可逆裂解为质子和电子。这里,我们通过IR和EPR光谱研究了温度和光照对耐氧和热稳定的[NiFe]氢化酶的影响。两种催化[NiFe]态的平衡混合物，Nia-C和Nia-SR\'\',被发现随温度急剧变化，表明[NiFe]活性位点与酶的铁硫簇之间的电子热交换。此外,在光照下进行的IR和EPR实验揭示了酶的异常光化学响应。Nia-SR\'\',催化循环的完全还原的氢化物中间体，被发现可逆地转化为另一种催化状态，Nia-L.与众所周知的氧化氢化物中间体Nia-C的光解相反，将Nia-SR光转化为Nia-L是一种活性位点氧化还原反应，涉及光驱动的电子向酶的铁硫簇转移。省略基态中间Nia-C，这两种状态的这种直接相互转换代表了催化循环的潜在光化学捷径，它整合了酶的多个氧化还原位点。总的来说,我们的发现揭示了电子通过热和光化学反应通道的非局部再分布，以及通过光加速或控制[NiFe]氢化酶的潜力。
