Spectroscopic characterization of a manganese–lignin peroxidase hybrid isozyme produced by Bjerkandera adusta in the absence of manganese: evidence of a protein centred radical by hydrogen peroxide

Electronic absorption and electron paramagnetic resonance (EPR) spectra are reported for a novel manganese–lignin peroxidase (MnLiP) hybrid isozyme produced by Bjerkandera adusta in the absence of manganese at pH 5. The room temperature absorption and the low temperature (10 K) EPR spectra indicate that the same coordination and spin states are present at both temperatures: mainly six coordinate high spin containing low percentage six coordinate low spin ferric heme, the latter probably with a bis-imidazole coordination. A protein centred radical was detected in the presence of an excess of hydrogen peroxide and assumed to be a tryptophanyl radical. The catalytic significance of this site was addressed by specific chemical modification of the tryptophan residues that revealed a marked effect on the specific activity of the enzyme. It is proposed that substrate oxidation might proceed through a long range-electron transfer process.