NITROGEN AND PROTON ENDOR OF CYTOCHROME-D, HEMIN, AND METMYOGLOBIN INFROZEN-SOLUTIONS

Orientation-selected electron nuclear double resonance (ENDOR) spectra have been obtained from iron-linked nitrogens of the d heme of the cy tochrome d oxidase complex in frozen solution. Heme d is a high-spin c hlorin moiety which exists in the cytochrome d complex located in the inner membrane of Escherichia coli. This complex is a terminal oxidase in the E. coli aerobic respiratory chain. Comparison of the spectra o f cytochrome d with hemin and metmyoglobin strongly implies that the d heme does not contain an axial nitrogen ligand. By computer simulatio n of the ENDOR spectra for each magnetic field, the nitrogen hyperfine interaction matrices and quadrupole coupling tensors to the three hem e groups were determined. For each of the three heme groups studied, t he proton hyperfine coupling perpendicular to the heme plane was also measured. From average hyperfine coupling constants, the unpaired elec tron densities in the nitrogen 2s and 2p valence orbitals were calcula ted with standard ligand field techniques. The quadrupole constants ar e also related to electron populations in the nitrogen orbitals. The c omparison between theoretical calculations and experimental data is sh own.