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Molecules 2018, 23(7), 1669; https://doi.org/10.3390/molecules23071669

Spectroscopical Investigations on the Redox Chemistry of [FeFe]-Hydrogenases in the Presence of Carbon Monoxide

1
Department of Physics, Experimental Molecular Biophysics, Freie Universität Berlin, 14195 Berlin, Germany
2
Department of Physics, Biophysics of Metalloenzymes, Freie Universität Berlin, 14195 Berlin, Germany
3
Faculty of Biology and Biotechnology, Photobiotechnology, Ruhr-Universität Bochum, 44801 Bochum, Germany
4
Faculty of Chemistry and Biochemistry, Inorganic Chemistry I, Ruhr-Universität Bochum, 44801 Bochum, Germany
5
Fraunhofer UMSICHT, Osterfelder Straße 3, 46047 Oberhausen, Germany
*
Authors to whom correspondence should be addressed.
Received: 19 June 2018 / Revised: 4 July 2018 / Accepted: 6 July 2018 / Published: 9 July 2018
(This article belongs to the Special Issue Metal Complexes of Biological Ligands)
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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. View Full-Text
Keywords: metalloenzymes; FTIR spectro-electrochemistry; hydrogenases metalloenzymes; FTIR spectro-electrochemistry; hydrogenases
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Laun, K.; Mebs, S.; Duan, J.; Wittkamp, F.; Apfel, U.-P.; Happe, T.; Winkler, M.; Haumann, M.; Stripp, S.T. Spectroscopical Investigations on the Redox Chemistry of [FeFe]-Hydrogenases in the Presence of Carbon Monoxide. Molecules 2018, 23, 1669.

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