Resonance raman study on axial ligands of heme irons in cytochrome bd‐type ubiquinol oxidase from Escherichia coli

Resonance Raman (RR) spectra of cytochrome bd‐type ubiquinol oxidase enriched with Fe‐isotopes were investigated with excitation at 406.7, 424.0, 427.0, 441.6, and 647.1 nm. The bands of reduced form at 252 and 400 cm⁻¹ were tentatively assigned to v_FeHis of high‐spin b₅₉₅ and v_FeMet of low‐spin b₅₅₈, respectively. The v FeO 2 and δ_FeOO bands of heme d‐O₂ were observed at 566 and ∼445 cm₋₁, respectively. The v_FeCO frequency of heme d‐CO was unusually low (477 cm⁻¹) but the v₄ frequency was not of P‐450 type. Therefore, the axial ligand of heme d would not be an ordinary histidine or cysteine. © 1995 John Wiley & Sons, Inc.