Oxidation of polycyclic aromatic hydrocarbons and dibenzo[p]-dioxins by Phanerochaete chrysosporium ligninase.

K E Hammel,B Kalyanaraman,T K Kirk

doi:10.1016/s0021-9258(19)75982-1

Abstract

The lignin peroxidase (ligninase) of Phanerochaete chrysosporium catalyzes the oxidation of a variety of lignin-related compounds. Here we report that this enzyme also catalyzes the oxidation of certain aromatic pollutants and compounds related to them, including polycyclic aromatic hydrocarbons with ionization potentials less than or equal to approximately 7.55 eV. This result demonstrates that the H2O2-oxidized states of lignin peroxidase are more oxidizing than the analogous states of classical peroxidases. Experiments with pyrene as the substrate showed that pyrene-1,6-dione and pyrene-1,8-dione are the major oxidation products (84% of total as determined by high performance liquid chromatography), and gas chromatography/mass spectrometry analysis of ligninase-catalyzed pyrene oxidations done in the presence of H2(18)O showed that the quinone oxygens come from water. We found that whole cultures of P. chrysosporium also transiently oxidize pyrene to these quinones. Experiments with dibenzo[p]dioxin and 2-chlorodibenzo[p]dioxin showed that they are also substrates for ligninase. The immediate product of dibenzo[p]dioxin oxidation is the dibenzo[p]dioxin cation radical, which was observed in enzymatic reactions by its electron spin resonance and visible absorption spectra. The cation radical mechanism of ligninase thus applies not only to lignin, but also to other environmentally significant aromatics.

Highlights

The lignin peroxidaseof Phanerochaete hemoprotein peroxidases [5,6,7,8,9], and it has been chrysosporium catalyzes the oxidationof a variety of proposed that these enzymes might be involved in pollutant lignin-relatedcompounds.Here we reportthat this oxidation [2]
Cation radical, which was observed in enzymatic reactions by its electron spin resonance and visible ab
The cation radical mechanisomf lig- form of the enzyme produced under these culture conditions, was ninase applies not onlylitgonin, and to other purified by ion exchange HPLC on Pharmacia Mono Q [16]

Summary

Introduction

The lignin peroxidase (ligninase)of Phanerochaete hemoprotein peroxidases (ligninases) [5,6,7,8,9], and it has been chrysosporium catalyzes the oxidationof a variety of proposed that these enzymes might be involved in pollutant lignin-relatedcompounds.Here we reportthat this oxidation [2]. ‘“0Labeling Studies-H;”O-labeling investigations of enzymatic pyrene oxidation were done in reaction mixtures with ligninase and Pyrene Oxidation by Fungal Cultures-For studies of pyrene metabolism by whole cultures of P. chrysosporium,the PAH was added (4.5 p~ final concentration) in a small volume of N,N-dimethylformamide at thetime of spore inoculation.

Results

Conclusion