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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
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 (, 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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