Observation of the Fe⁴⁺=O stretching Raman band for cytochrome oxidase compound B at ambient temperature

Resonance Raman and visible absorption spectra were simultaneously observed for cytochrome oxidase reaction intermediates at 5°C by using the artificial cardiovascular system (Ogura, T., Yoshikawa, S., and Kitagawa, T. (1989) Biochemistry 28, 8022-8027) and a device for Raman/absorption simultaneous measurements (Ogura, T., and Kitagawa, T. (1988) Rev. Sci. Instrum. 59, 1316-1320). The Fe⁴⁺=O stretching (ν(FeO)) Raman band was observed at 788 cm^-1 for compound B for the first time. This band showed the ¹⁶O/¹⁸O isotopic frequency shift (Δν(FeO)) by 40 cm^-1, in agreement with that for horseradish peroxidase compound II (ν(FeO) = 787 cm^-1 and Δν(FeO) = 34 cm^-a1). In the time region when the Fe(II)-O₂ stretching band for compound A and the ν(FeO) band for compound B were coexistent, a Raman band assignable to the Fe³⁺-O-O-Cu²⁺ linkage was not recognized.