[FeFe]-hydrogenases catalyze the reversible oxidation of H from electrons and protons at an organometallic active site cofactor named the H-cluster. In addition to the H-cluster, most [FeFe]-hydrogenases possess accessory FeS cluster (F-cluster) relays that function in mediating electron transfer with catalysis. There is significant variation in the structural properties of F-cluster relays among the [FeFe]-hydrogenases; however, it is unknown how this variation relates to the electronic and thermodynamic properties, and thus the electron transfer properties, of enzymes. [FeFe]-hydrogenase II (CpII) exhibits a large catalytic bias for H oxidation (compared to H production), making it a notable system for examining if F-cluster properties contribute to the overall function and efficiency of the enzyme. By applying a combination of multifrequency and potentiometric electron paramagnetic resonance, we resolved two electron paramagnetic resonance signals with distinct power- and temperature-dependent properties at = 2.058 1.931 1.891 (F) and = 2.061 1.920 1.887 (F), with assigned midpoint potentials of −140 ± 18 mV and −406 ± 12 mV normal hydrogen electrode, respectively. Spectral analysis revealed features consistent with spin-spin coupling between the two [4Fe-4S] F-clusters, and possible functional models are discussed that account for the contribution of coupling to the electron transfer landscape. The results signify the interplay of electronic coupling and free energy properties and parameters of the FeS clusters to the electron transfer mechanism through the relay and provide new insight as to how relays functionally complement the catalytic directionality of active sites to achieve highly efficient catalysis.

中文翻译：

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[FeFe]-氢化酶中铁硫簇电子传递继电器的特性，该酶针对 H2 氧化催化进行了调整


[FeFe]-氢化酶在称为 H-簇的有机金属活性位点辅助因子上催化电子和质子对 H 的可逆氧化。除了 H 簇之外，大多数 [FeFe]-氢化酶还具有辅助 FeS 簇（F 簇）中继，其功能是通过催化介导电子转移。 [FeFe]-氢化酶之间的 F 簇中继结构特性存在显着差异；然而，尚不清楚这种变化如何与酶的电子和热力学特性以及电子转移特性相关。 [FeFe]-氢化酶 II (CpII) 对 H 氧化（与 H 产生相比）表现出较大的催化偏差，使其成为检查 F 簇特性是否有助于酶的整体功能和效率的重要系统。通过应用多频和电位电子顺磁共振的组合，我们在 = 2.058 1.931 1.891 (F) 和 = 2.061 1.920 1.887 (F) 处解析了具有不同功率和温度依赖性特性的两个电子顺磁共振信号，指定的中点电位为分别为-140±18mV和-406±12mV标准氢电极。光谱分析揭示了与两个 [4Fe-4S] F 团簇之间的自旋-自旋耦合一致的特征，并讨论了解释耦合对电子转移景观的贡献的可能的功能模型。结果表明，FeS簇的电子耦合和自由能性质以及参数与通过继电器的电子转移机制之间的相互作用，并为继电器如何在功能上补充活性位点的催化方向性以实现高效催化提供了新的见解。