Resonance raman spectra of native and mesoheme-reconstituted horseradish peroxidase and their catalytic intermediates

Abstract

Resonance Raman studies of native and mesoheme-reconstituted horseradish peroxidase and their catalytic intermediates, known as Compounds I and II, have been conducted using both near UV (~350 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 H218O2, the ν(Fe=O) stretching modes for both systems are unambiguously identified, for the first time, at ~790 cm-1. The authentic Compound I spectra are indicative of an 2A(1u)-like ground state for both the native and the mesoheme-reconstituted proteins. Finally, the possible biological implications of such information are briefly discussed.