Photoperturbation of the Heme a₃-Cu_B Binuclear Center of Cytochrome c Oxidase CO Complex Observed by Fourier Transform Infrared Spectroscopy

Sungjo Park, Lian-Ping Pan, Sunney I. Chan, and James O. Alben Biophysical Journal 71: 1036-1047, 1996

SUMMARY: Purified cytochrome c oxidase CO complex from beef heart has been studied by Fourier transform infrared absorbance difference spectroscopy. Photolysis at 10Ð20 Kelvin results in dissociation of a₃FeCO, formation of Cu_BCO, and perturbation of the a₃-heme and Cu_B complex. The (light minus dark) vibrational perturbation spectrum between 900 and 1700 cm^-1 contains a wealth of information about the binuclear center. Appearance in infrared photoperturbation difference spectra of virtually all bands previously reported from resonance Raman spectra indicate the importance of polarization along the 4-finyl:8-formyl axis, which results in the reduction of heme symmetry to C_2V. Frequency-shifted bands due to the 8-formyl and 4-vinyl groups of the a₃-heme have been identified and quantitated. The frequency shifts have been interpreted as being due to a change in porphyrin polarization with change in spin state of the iron by photodissociation of CO or perturbation of the Cu_B coordination complex. (Useful tables of assignments on CcO and model compounds are given).