Oxygen exchange between the Fe(IV)O heme and bulk water for the A2 isozyme of horseradish peroxidase

Abstract
Resonance Raman spectra were observed for compound II of horseradish peroxidase A2, and the Fe(IV)O stretching Raman line was identified at 775 cm−1. This Raman line shifted to 741 cm−1 upon a change of solvent from H2 16O to H2 18O, indicating occurrence of the oxygen exchange between the Fe(IV)O heme and bulk water. The oxygen exchange took place only at the acidic side of the heme‐linked ionization with pK a = 6.9.