Resonance Raman spectroscopy of cytochrome oxidase using Soret excitation: selective enhancement, indicator bands, and structural significance for cytochromes a and a3

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Abstract
Resonance Raman studies of oxidized and reduced [beef heart] cytochrome oxidase and liganded derivatives of the oxidized enzyme were performed by using direct-Soret excitation at 413.1 and 406.7 nm, as well as near-Soret excitation (457.9 nm) and .alpha.-band excitation (604.6 nm). The Soret results clearly show selective enhancement of Raman modes of the hemes of cytochromes a and a3, depending upon the excitation wavelength chosen. For the preparations employed in this study, photoreduction of cytochrome oxidase in the laser beam was not a significant problem. Resonance Raman frequencies sensitive to oxidation state and spin state or core expansion of the a and a3 hemes are identified and correlated with those previously identified for other heme proteins. An unusual low-frequency (< 500 cm-1) spectrum is observed for oxidized high-spin cytochrome a3, which may be due to axial nonheme structures in this cytochrome.

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