Discovery of Dark pH-Dependent H(+) Migration in a [NiFe]-Hydrogenase and Its Mechanistic Relevance: Mobilizing the Hydrido Ligand of the Ni-C Intermediate.
J Am Chem Soc
; 137(26): 8484-9, 2015 Jul 08.
Article
em En
| MEDLINE
| ID: mdl-26103582
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.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Carbono
/
Proteínas de Escherichia coli
/
Hidrogenase
/
Nitrogênio
Idioma:
En
Ano de publicação:
2015
Tipo de documento:
Article