title: Tetrahedral iron in the active center of plant ferredoxins and beef adrenodoxin.
abstract: The coordination structure of the iron-sulfur complex in spinach ferredoxin and adrenodoxin is investigated by optical spectroscopy. The circular-dichroism and absorption spectra of these two-iron iron-sulfur proteins reveal weak electronic transitions in the near-infrared wavelength range, 0.8-2.5 mum (12,500-4000 cm(-1)). On the basis of the low absorption intensities and large anisotropy factors, d --> d transitions of the iron can be identified in the reduced proteins at about 4000 cm(-1) and 6000 cm(-1). The low energy of these one-center ligand-field transitions, together with the similarity to the ligand-field spectrum of the one-iron protein rubredoxin, leads to the conclusion that the reduced two-iron iron-sulfur proteins also contain a high-spin ferrous ion in a distorted tetrahedral site.
mesh_terms: D000311:Adrenal Glands; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002736:Chloroplasts; D002942:Circular Dichroism; D003013:Clostridium; D004578:Electron Spin Resonance Spectroscopy; D005288:Ferredoxins; D007259:Infrared Rays; D007501:Iron; D008961:Models, Structural; D010084:Oxidation-Reduction; D010940:Plant Proteins; D013057:Spectrum Analysis; D013455:Sulfur
chemical_list: D005288:Ferredoxins; D010940:Plant Proteins; D013455:Sulfur; D007501:Iron