RESONANCE RAMAN-SPECTRA OF NATIVE AND MESOHEME-RECONSTITUTED HORSERADISH-PEROXIDASE AND THEIR CATALYTIC INTERMEDIATES

Resonance Raman studies of native and mesohemere-constituted horseradi sh peroxidase and their catalytic intermediates, known as Compounds I and II, have been conducted using both near UV (similar to 350 nm) and visible (406.7 nm) excitation. Careful power studies indicate that th e authentic Compound I spectra are obtainable using near UV excitation , but that use of visible excitation results in contamination of the C ompound I spectrum with the spectrum of a Compound II-like photoproduc t. Using (H2O2)-O-18, the nu(Fe=O) stretching modes for both systems a re unambiguously identified, for the first time, at similar to 790 cm( -1). The authentic Compound I spectra are indicative of an (2)A(1u)-li ke ground state for both the native and the mesoheme-reconstituted pro teins. Finally, the possible biological implications of such informati on are briefly discussed.