Resonance Raman Study on the Structure in the Heme Vicinity of Peroxidases

Abstract

Resonance Raman spectra of horseradish peroxidase (HRP) and yeast cytochrome c peroxidase (CcP) were observed and the structure in the heme vicinity characteristic of peroxidases, was discussed. The resonance Raman spectra of reaction intermediates were also observed and the Fe⁴⁺=O stretching band was assigned on the basis of the isotope shifts. It became clear that the sixth ligand of the Fe⁴⁺ heme of the intermediate was not the OH group but the 0 atom, and that the iron-bound oxygen atom was exchanged with that of solvent wh ile the measurements were carried out (3 min). This oxygen-exchange reaction took place only with the acidic form in which the proton involved in the heme-linked ionization was hydrogen-bonded to the iron-bound oxygen and the pH dependence of the exchange reaction appeared in parallel with the enzymic activity.