Similarities in the architecture of the active sites of Ni-hydrogenases and Fe-hydrogenases detected by means of infrared spectroscopy.

Three groups that absorb in the 2100-1800-cm-1 infrared spectral region have recently been detected in Ni-hydrogenase from Chromatium vinosum [Bagley, K.A., Duin, E.C., Roseboom, W., Albracht, S. P.J. & Woodruff, W.H. (1995) Biochemistry 34, 5527-5535]. To assess the significance and generality of this observation, we have carried out an infrared-spectroscopic study of eight hydrogenases of three different types (nickel, iron and metal-free) and of 11 other iron-sulfur and/or nickel proteins. Infrared bands in the 2100-1800-cm-1 spectral region were found in spectra of all Ni-hydrogenases and Fe-hydrogenases and were absent from spectra of any of the other proteins, including a metal-free hydrogenase. The positions of these bands are dependent on the redox state of the hydrogenase. The three groups in Ni-hydrogenases that are detected by infrared spectroscopy are assigned to the three unidentified small non-protein ligands that coordinate iron in the dinuclear Ni/Fe active site as observed in the X-ray structure of the enzyme from Desulfovibrio gigas [Volbeda, A., Charon, M.-H., Piras, C., Hatchikian, E.C., Frey, M. & Fontecilla-Camps, J.C. (1995) Nature 373, 580-587]. It is concluded that these groups occur exclusively in metal-containing H2-activating enzymes. It is proposed that the active sites of Ni-hydrogenases and of Fe-hydrogenases have a similar architecture, that is required for the activation of molecular hydrogen.