SYNOPSISResonance Raman ( R R ) 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 hands of reduced form a t 252 and 400 cm-' were tentatively assigned to u p e -~i s of high-spin bSg5 and vFePMet of low-spin respectively. The uFe-O, and 6FeO0 bands of heme d-O2 were observed at 566 and -445 cm-', respectively. The vpe-cO frequency of heme d -CO was unusually low (477 cm-') but the u4 frequency was not of P-450 type. Therefore, the axial ligand of heme d would not be an ordinary histidine or cysteine. 0 1995 John