Resonance Raman Studies on Heme Ligand Stretching Modes in Methionine80-Depleted Cytochrome : Fe-His, Fe-O, and O-O Stretching Modes.

The peroxidase activity of cytochrome (cyt) increases when Met80 dissociates from the heme iron, which is related to the initial cyt membrane permeation step of apoptosis. Met80-dissociated cyt can form an oxygenated species. Herein, resonance Raman spectra of Met80-depleted horse cyt (M80A cyt ) were analyzed to elucidate the heme ligand properties of Met80-dissociated cyt . The Fe-His stretching (ν) mode of ferrous M80A cyt was observed at 236 cm, and this frequency decreased by 1.5 cm for the N-labeled protein. The higher ν frequency of M80A cyt than of other His-ligated heme proteins indicates strong heme coordination and the imidazolate character of His18. Peaks attributed to the Fe-O stretching (ν) and O-O stretching (ν) modes of the oxygenated species of M80A cyt were observed at 576 and 1148 cm, respectively, under an O atmosphere, whereas the frequencies decreased to 544 and 1077 cm, respectively, under an O atmosphere. The ν mode of (HT) M59A cyt was observed at 580 cm under an O atmosphere, whereas the frequency decreased to 553 cm under an O atmosphere, indicating that relatively high ν frequencies are characteristic of -type cyt proteins. By comparison of the simultaneously observed ν and ν frequencies of oxygenated cyt and other oxygenated His-ligated heme proteins, the frequencies tend to have a positive linear relationship; the ν frequency increases when the ν frequency increases. The imidazolate character of the heme-coordinated His and strong Fe-O and O-O bonds are characteristic of cyt and apparently related to the peroxidase activity when Met80 dissociates from the heme iron.