Please use this identifier to cite or link to this item: http://hdl.handle.net/2381/44457
Title: Discovery of Dark pH-Dependent H(+) Migration in a [NiFe]-Hydrogenase and Its Mechanistic Relevance: Mobilizing the Hydrido Ligand of the Ni-C Intermediate.
Authors: Murphy, BJ
Hidalgo, R
Roessler, MM
Evans, RM
Ash, PA
Myers, WK
Vincent, KA
Armstrong, FA
First Published: 23-Jun-2015
Publisher: American Chemical Society
Citation: Journal of the American Chemical Society, 2015, 137 (26), pp. 8484-8489
Abstract: Despite extensive studies on [NiFe]-hydrogenases, the mechanism by which these enzymes produce and activate H2 so efficiently remains unclear. A well-known EPR-active state produced under H2 and known as Ni-C is assigned as a Ni(III)-Fe(II) species with a hydrido ligand in the bridging position between the two metals. It has long been known that low-temperature photolysis of Ni-C yields distinctive EPR-active states, collectively termed Ni-L, that are attributed to migration of the bridging-H species as a proton; however, Ni-L has mainly been regarded as an artifact with no mechanistic relevance. It is now demonstrated, based on EPR and infrared spectroscopic studies, that the Ni-C to Ni-L interconversion in Hydrogenase-1 (Hyd-1) from Escherichia coli is a pH-dependent process that proceeds readily in the dark-proton migration from Ni-C being favored as the pH is increased. The persistence of Ni-L in Hyd-1 must relate to unassigned differences in proton affinities of metal and adjacent amino acid sites, although the unusually high reduction potentials of the adjacent Fe-S centers in this O2-tolerant hydrogenase might also be a contributory factor, impeding elementary electron transfer off the [NiFe] site after proton departure. The results provide compelling evidence that Ni-L is a true, albeit elusive, catalytic intermediate of [NiFe]-hydrogenases.
DOI Link: 10.1021/jacs.5b03182
eISSN: 1520-5126
Links: https://pubs.acs.org/doi/10.1021/jacs.5b03182
http://hdl.handle.net/2381/44457
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © the authors, 2015. This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Description: Infrared spectra of Hyd-1 adsorbed on carbon black particles before and after activation under H2. Graph showing how the potential at which the Ni-C and Ni-L peaks have maximum combined intensity varies as a function of solution pH. X-band HYSCORE spectra of a wild-type Hyd-1 sample, pH 4.0, at g = 2.18, before and after illumination. X-band CW EPR spectra of Hyd-1 at pH 3.0, showing the effect of illumination. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.5b03182.
Appears in Collections:Published Articles, Dept. of Chemistry



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