Resonance Raman studies of native and mesohemereconstituted horseradish peroxidase and their catalytic intermediates, known as Compounds I and II, have been conducted using both near UV (ϳ350 nm) and visible (406.7 nm) excitation. Careful power studies indicate that the authentic Compound I spectra are obtainable using near UV excitation, but that use of visible excitation results in contamination of the Compound I spectrum with the spectrum of a Compound II-like photoproduct. Using H 2 18 O 2 , the (Fe‫؍‬O) stretching modes for both systems are unambiguously identified, for the first time, at ϳ790 cm ؊1 . The authentic Compound I spectra are indicative of an 2 A 1u -like ground state for both the native and the mesoheme-reconstituted proteins. Finally, the possible biological implications of such information are briefly discussed.

Abstract

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