Resonance Raman Studies on Heme Ligand Stretching Modes in Methionine80-Depleted Cytochrome c: Fe-His, Fe-O₂, and O-O Stretching Modes.

ABSTRACT: The peroxidase activity of cytochrome (cyt) c increases when Met80 dissociates from the heme iron, which is related to the initial cyt c membrane permeation step of apoptosis. Met80-dissociated cyt c can form an oxygenated species. Herein, resonance Raman spectra of Met80-depleted horse cyt c (M80A cyt c) were analyzed to elucidate the heme ligand properties of Met80-dissociated cyt c. The Fe-His stretching (ν_Fe-His) mode of ferrous M80A cyt c was observed at 236 cm^-1, and this frequency decreased by 1.5 cm^-1 for the ¹⁵N-labeled protein. The higher ν_Fe-His frequency of M80A cyt c than of other His-ligated heme proteins indicates strong heme coordination and the imidazolate character of His18. Peaks attributed to the Fe-O₂ stretching (ν_Fe-O2) and O-O stretching (ν_O-O) modes of the oxygenated species of M80A cyt c were observed at 576 and 1148 cm^-1, respectively, under an ¹⁶O₂ atmosphere, whereas the frequencies decreased to 544 and 1077 cm^-1, respectively, under an ¹⁸O₂ atmosphere. The ν_Fe-O2 mode of Hydrogenobacter thermophilus (HT) M59A cyt c₅₅₂ was observed at 580 cm^-1 under an ¹⁶O₂ atmosphere, whereas the frequency decreased to 553 cm^-1 under an ¹⁸O₂ atmosphere, indicating that relatively high ν_Fe-O2 frequencies are characteristic of c-type cyt proteins. By comparison of the simultaneously observed ν_Fe-O2 and ν_O-O frequencies of oxygenated cyt c and other oxygenated His-ligated heme proteins, the frequencies tend to have a positive linear relationship; the ν_Fe-O2 frequency increases when the ν_O-O frequency increases. The imidazolate character of the heme-coordinated His and strong Fe-O and O-O bonds are characteristic of cyt c and apparently related to the peroxidase activity when Met80 dissociates from the heme iron.

SUBMITTER: Zhang M 

PROVIDER: S-EPMC10041640 | biostudies-literature | 2023 Mar

REPOSITORIES: biostudies-literature