Identification of Fe(III)–OH species as a catalytic intermediate in plant peroxidases at high H2O2 concentration

The structural determinants underlying the instability of plant peroxidases toward H2O2 are unknown. The reaction of the catalytically productive radical Fe(IV)QO species with excess H2O2 generates a species named compound III, which is known to decay partitioning between ground state restoration and inactivation following catalytical suicide kinetics. To elucidate the structural changes involved in compound III formation and decay, here we report the characterization of two plant peroxidases using catalytic and spectroscopic characterization. Resonance Raman and EPR characterizations reveal that the structure of compound III is more related to the hydroxyl form of other heme proteins and not to the peroxyferryl form as has been previously suggested.