Determination of Qx- and Qy- absorption bands of Zn-porphyrin derivatives contained in proteins by hole-burning spectroscopy

The Qx- and Qy- absorption components of Zn-protoporphyrin and Zn-mesoporphyrin substituted respectively in myoglobin and cytochrome C have been extracted from inhomogeneously broadened absorption spectra by means of polarization-dependent transient hole-burning spectroscopy. The splitting between these components has been obtained as ∼330 cm−1 and ∼230 cm−1 for myoglobin and cytochrome C, respectively. The intensities of these two bands are much different in the case of myoglobin, while they have comparative intensities in the case of cytochrome C. It has been suggested that the porphyrin molecule feels much stronger local field in myoglobin than in cytochrome C.