Abstract
[FeFe]-hydrogenases efficiently catalyzes hydrogen conversion at a unique [4Fe–4S]-[FeFe] cofactor, the so-called H-cluster. The catalytic reaction occurs at the diiron site, while the [4Fe–4S] cluster functions as a redox shuttle. In the oxidized resting state (Hox), the iron ions of the diiron site bind one cyanide (CN−) and carbon monoxide (CO) ligand each and a third carbonyl can be found in the Fe–Fe bridging position (µCO). In the presence of exogenous CO, A fourth CO ligand binds at the diiron site to form the oxidized, CO-inhibited H-cluster (Hox-CO). We investigated the reduced, CO-inhibited H-cluster (Hred´-CO) in this work. The stretching vibrations of the diatomic ligands were monitored by attenuated total reflection Fourier-transform infrared spectroscopy (ATR FTIR). Density functional theory (DFT) at the TPSSh/TZVP level was employed to analyze the cofactor geometry, as well as the redox and protonation state of the H-cluster. Selective 13CO isotope editing, spectro-electrochemistry, and correlation analysis of IR data identified a one-electron reduced, protonated [4Fe–4S] cluster and an apical CN− ligand at the diiron site in Hred´-CO. The reduced, CO-inhibited H-cluster forms independently of the sequence of CO binding and cofactor reduction, which implies that the ligand rearrangement at the diiron site upon CO inhibition is independent of the redox and protonation state of the [4Fe–4S] cluster. The relation of coordination dynamics to cofactor redox and protonation changes in hydrogen conversion catalysis and inhibition is discussed.
Highlights
Hydrogenases [1] are remarkably efficient catalysts for hydrogen conversion with significant potential in renewable energy applications [2,3,4]
In comparison with Hox, our analysis suggests that Hred-carbon monoxide (CO) and
The catalytically competent enzyme was injected onto a thin gold mesh that was used to cover the silicon crystal of an ATR cell
Summary
Hydrogenases [1] are remarkably efficient catalysts for hydrogen conversion with significant potential in renewable energy applications [2,3,4]. Hydrogenase proteins have been extensively characterized by X-ray. Hydrogenase proteins have been extensively characterized by X-ray crystallography [5], protein film electrochemistry [11,12,13], and numerous spectroscopic crystallography [5],protein film [11,12,13], and numerous spectroscopic techniques techniques [14]. Theelectrochemistry relations between coordination dynamics at the active site and [14]. The relations between coordination dynamics at the active site and redox chemistry are still chemistry are still under debate [15]. [FeFe]-hydrogenases are found in archaea, bacteria, and unicellular algae [16]. They show truly [FeFe]-hydrogenases are found in(i.e., archaea, bacteria, unicellular algae [16] They show truly bidirectional hydrogen conversion catalysis of Hand
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