RESONANCE RAMAN STUDIES OF NICKEL TETRATHIOLATES AND NICKEL-SUBSTITUTED RUBREDOXINS AND DESULFOREDOXIN

Low-temperature resonance Raman spectroscopy has been used to investigate the nickel coordination geometry in the [Ni(SPh)4]2- anion in solution, Ni(II)-substituted rubredoxins from Desulfovibrio gigas and Pyrococcus furiosus, and Ni(II)-substituted desulforedoxin from D. gigas. Ni-S vibrational modes have been assigned on the basis of Ni-58/Ni-60 isotope shifts, polarization studies, and comparison with structurally characterized tetrathiolate Ni(II) complexes. The results indicate tetragonally elongated tetrahedral [NiS4] cores in the [Ni(SPh)4]2- anion in solution and in both Ni(II)-rubredoxins and a distorted square planar [NiS4] core in Ni(II)-desulforedoxin. Cysteine deformation modes that are enhanced via coupling with Ni-S stretching modes are observed near 400 cm-1 in the spectra of both native and Ni(II)-substituted rubredoxins. The potential of resonance Raman for investigating Ni-cysteinate centers in other metalloproteins and for elucidating the conformation of coordinating cysteine residues is discussed in light of these new results.