title: Probing intermediates in the activation cycle of [NiFe] hydrogenase by infrared spectroscopy: the Ni-SIr state and its light sensitivity.
abstract: The [NiFe] hydrogenase from the sulphate-reducing bacterium Desulfovibrio vulgaris Miyazaki F is reversibly inhibited in the presence of molecular oxygen. A key intermediate in the reactivation process, Ni-SI(r), provides the link between fully oxidized (Ni-A, Ni-B) and active (Ni-SI(a), Ni-C and Ni-R) forms of hydrogenase. In this work Ni-SI(r) was found to be light-sensitive (T <or= 110 K), similar to the active Ni-C and the CO-inhibited states. Transition to the final photoproduct state (Ni-SL) was shown to involve an additional transient light-induced state (Ni-SI(1961)). Rapid scan kinetic infrared measurements provided activation energies for the transition from Ni-SL to Ni-SI(r) in protonated as well as in deuterated samples. The inhibitor CO was found not to react with the active site of the Ni-SL state. The wavelength dependence of the Ni-SI(r) photoconversion was examined in the range between 410 and 680 nm. Light-induced effects were associated with a nickel-centred electronic transition, possibly involving a change in the spin state of nickel (Ni(2+)). In addition, at T <or= 40 K the CN(-) stretching vibrations of Ni-SL were found to be dependent on the colour of the monochromatic light used to irradiate the species, suggesting a change in the interaction of the hydrogen-bonding network of the surrounding amino acids. A possible mechanism for the photochemical process, involving displacement of the oxygen-based ligand, is discussed.
authors.affiliation: Max-Planck-Institut für Bioanorganische Chemie, 45470 Mülheim an der Ruhr, Germany.
authors.forename: Maria-Eirini
authors.initials: ME
authors.lastname: Pandelia
authors.forename: Hideaki
authors.initials: H
authors.lastname: Ogata
authors.forename: Leslie J
authors.initials: LJ
authors.lastname: Currell
authors.forename: Marco
authors.initials: M
authors.lastname: Flores
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lubitz
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D002248:Carbon Monoxide / Q000378:metabolism; D016969:Desulfovibrio vulgaris / Q000201:enzymology*; D004789:Enzyme Activation; D006860:Hydrogen Bonding; D006864:Hydrogenase / Q000737:chemistry / Q000378:metabolism*; D007554:Isotopes / Q000378:metabolism; D008027:Light; D008958:Models, Molecular; D009532:Nickel / Q000378:metabolism*; D010084:Oxidation-Reduction; D011487:Protein Conformation; D013055:Spectrophotometry, Infrared; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D001426:Bacterial Proteins; D007554:Isotopes; D009532:Nickel; D002248:Carbon Monoxide; C043296:nickel-iron hydrogenase; D006864:Hydrogenase