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Title: CO-Bridged H-Cluster Intermediates in the Catalytic Mechanism of [FeFe]-Hydrogenase CaI

Abstract

The [FeFe]-hydrogenases ([FeFe] H 2ases) catalyze reversible H 2 activation at the H-cluster, which is composed of a [4Fe-4S] H subsite linked by a cysteine thiolate to a bridged, organometallic [2Fe-2S] ([2Fe] H) subsite. Profoundly different geometric models of the H-cluster redox states that orchestrate the electron/proton transfer steps of H 2 bond activation have been proposed. We have examined this question in the [FeFe] H 2ase I from Clostridium acetobutylicum (CaI) by Fourier-transform infrared (FTIR) spectroscopy with temperature annealing and H/D isotope exchange to identify the relevant redox states and define catalytic transitions. One-electron reduction of H ox led to formation of H redH + ([4Fe-4S] H 2+-Fe I-Fe I) and H red' ([4Fe-4S] H 1+-Fe II-Fe I), with both states characterized by low frequency μ-CO IR modes consistent with a fully bridged [2Fe] H. Similar μ-CO IR modes were also identified for H redH + of the [FeFe] H 2ase from Chlamydomonas reinhardtii (CrHydA1). The CaI proton-transfer variant C298S showed enrichment of an H/D isotope-sensitive μ-CO mode, a component of the hydride bound H-cluster IR signal, H hyd. Equilibrating CaI with increasing amounts of NaDT, and probed at cryogenic temperatures, showed H redH + was converted to Hmore » hyd. Over an increasing temperature range from 10 to 260 K catalytic turnover led to loss of Hhyd and appearance of H ox, consistent with enzymatic turnover and H 2 formation. The results show for CaI that the μ-CO of [2Fe] H remains bridging for all of the 'H red' states and that H redH + is on pathway to H hyd and H 2 evolution in the catalytic mechanism. Here, this provides a blueprint for designing small molecule catalytic analogs« less

Authors:
 [1];  [1];  [1];  [2];  [2]; ORCiD logo [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. Colorado School of Mines, Golden, CO (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1440310
Report Number(s):
NREL/JA-2700-71170
Journal ID: ISSN 0002-7863
Grant/Contract Number:
AC36-08GO28308
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 140; Journal Issue: 24; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; [FeFe]-hydrogenases; catalysis; catalytic transitions

Citation Formats

Ratzloff, Michael W., Artz, Jacob H., Mulder, David W., Collins, Reuben T., Furtak, Thomas E., and King, Paul W. CO-Bridged H-Cluster Intermediates in the Catalytic Mechanism of [FeFe]-Hydrogenase CaI. United States: N. p., 2018. Web. doi:10.1021/jacs.8b03072.
Ratzloff, Michael W., Artz, Jacob H., Mulder, David W., Collins, Reuben T., Furtak, Thomas E., & King, Paul W. CO-Bridged H-Cluster Intermediates in the Catalytic Mechanism of [FeFe]-Hydrogenase CaI. United States. doi:10.1021/jacs.8b03072.
Ratzloff, Michael W., Artz, Jacob H., Mulder, David W., Collins, Reuben T., Furtak, Thomas E., and King, Paul W. Wed . "CO-Bridged H-Cluster Intermediates in the Catalytic Mechanism of [FeFe]-Hydrogenase CaI". United States. doi:10.1021/jacs.8b03072.
@article{osti_1440310,
title = {CO-Bridged H-Cluster Intermediates in the Catalytic Mechanism of [FeFe]-Hydrogenase CaI},
author = {Ratzloff, Michael W. and Artz, Jacob H. and Mulder, David W. and Collins, Reuben T. and Furtak, Thomas E. and King, Paul W.},
abstractNote = {The [FeFe]-hydrogenases ([FeFe] H2ases) catalyze reversible H2 activation at the H-cluster, which is composed of a [4Fe-4S]H subsite linked by a cysteine thiolate to a bridged, organometallic [2Fe-2S] ([2Fe]H) subsite. Profoundly different geometric models of the H-cluster redox states that orchestrate the electron/proton transfer steps of H2 bond activation have been proposed. We have examined this question in the [FeFe] H2ase I from Clostridium acetobutylicum (CaI) by Fourier-transform infrared (FTIR) spectroscopy with temperature annealing and H/D isotope exchange to identify the relevant redox states and define catalytic transitions. One-electron reduction of Hox led to formation of HredH+ ([4Fe-4S]H2+-FeI-FeI) and Hred' ([4Fe-4S]H1+-FeII-FeI), with both states characterized by low frequency μ-CO IR modes consistent with a fully bridged [2Fe]H. Similar μ-CO IR modes were also identified for HredH+ of the [FeFe] H2ase from Chlamydomonas reinhardtii (CrHydA1). The CaI proton-transfer variant C298S showed enrichment of an H/D isotope-sensitive μ-CO mode, a component of the hydride bound H-cluster IR signal, Hhyd. Equilibrating CaI with increasing amounts of NaDT, and probed at cryogenic temperatures, showed HredH+ was converted to Hhyd. Over an increasing temperature range from 10 to 260 K catalytic turnover led to loss of Hhyd and appearance of Hox, consistent with enzymatic turnover and H2 formation. The results show for CaI that the μ-CO of [2Fe]H remains bridging for all of the 'Hred' states and that HredH+ is on pathway to Hhyd and H2 evolution in the catalytic mechanism. Here, this provides a blueprint for designing small molecule catalytic analogs},
doi = {10.1021/jacs.8b03072},
journal = {Journal of the American Chemical Society},
number = 24,
volume = 140,
place = {United States},
year = {Wed May 23 00:00:00 EDT 2018},
month = {Wed May 23 00:00:00 EDT 2018}
}

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