Comparative Raman studies of cytochrome b₅₆₂ and cytochrome c

Resonance Raman spectra (excited at 413.1 nm) and excitation profiles (Q‐band region) of cytochrome b₅₆₂ and cytochrome c were obtained with a sensitive vidicon multichannel Raman spectrometer.⁷ Comparison of the spectra reveals that two Raman lines at 690 and 700 cm⁻¹ in cytochrome c may be assigned to CS stretch of the thioether bridges, which are absent in cytochrome b₅₆₂. Four sets of doublet between 320 and 430 cm⁻¹ are unique in cytochrome c among various hemoproteins may indicate the existence of two subtly distinct heme structures alternating in the ground state of cytochrome c. This unique spectral feature was not observed in heme octapeptide (reduced form in 0.25 M N‐acetyl‐methionine) which also contains the covalent thioether linkages. In addition, we compare the excitation profiles of a depolarized porphyrin ring mode at ∼ 750 cm⁻¹ among cytochrome c, cytochrome b₅₆₂ and Ni etioporphyrin. The effect of a Jahn‐Teller distortion observed in the 750 cm⁻¹ profile of Ni etioporphyrin¹⁹ is shown to be absent in cytochrome c. The 750 cm⁻¹ profiles in the Q‐band region are interpreted in terms of Herzberg‐Teller (B) and nonadiabatic (D) contributions with or without an origin shift.