Resonance Raman spectroscopy and enhanced photoreducibility for the 420 nm pulsed form of cytochrome oxidase

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Abstract
Resonance Raman (RR) spectra, with 413.1 nm Kr+ laser excitation, are reported for cytochrome oxidase in resting, reduced, and 428 nm (oxygenated) forms, and for the first time, in the 420 nm (pulsed) forms [(1984) J. Biol. Chem. 259, 2073‐2076]. The differences between the resting, 420 nm, and 428 nm forms' RR spectra are small. All these forms contain FeIII only, as indicated by single v4 bands at ~1371 cm−1, and the reoxidized forms show partial conversion from high‐ to intermediate‐ or low‐spin heme a 3 (intensity shift from 1575 to 1588 cm−1 for v2). The 420 nm form differs strikingly from both the 428 nm and resting forms, however, in being much more readily photoreduced by the laser illumination. This property is linked to the protein conformational change believed to be responsible for the greater accessibility to exogenous ligands of the heme a 3 in the 420 nm form.