Oxidative degradation of polyaromatic hydrocarbons and their derivatives catalyzed directly by the yellow laccase from Pleurotus ostreatus D1

The catalytic activity of the yellow laccase from Pleurotus ostreatus D1 (YLPO) towards a range of nonphenolic aromatic compounds, including polyaromatic hydrocarbons (PAHs), their derivatives, and anthracene-like synthetic dyes, was investigated. YLPO did not catalyze the oxidation of the two-ring PAH naphthalene, but the naphthalene derivatives α- and β-naphthols, α-nitroso-β-naphthol, α-hydroxy-β-naphthoic acid, and α-naphthylamine were all good laccase substrates. YLPO degraded all the PAHs containing from three to five rings, with the following efficiencies: 91% for anthracene, 40% for pyrene, 95% for fluorene, 47% for fluoranthene, 82% for phenanthrene, and 100% for perylene. These efficiencies were higher than that observed for a blue laccase from the same fungus in both absence and presence of the typical synthetic mediators 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and 1-hydroxybenzotriazole (HBT) under the same experimental conditions. YLPO oxidized a model mixture of PAHs and all the synthetic dyes except anthrone. The same product of anthracene oxidation and various unidentified products of fluorene oxidation were observed in solutions of various solvents. Although the blue and yellow laccases of P. ostreatus D1 oxidized the typical phenolic substrates in a similar way, all the collected data show that the catalytic properties of the blue and yellow laccases towards nonphenolic substrates differed significantly. Further catalytic and structural studies are needed to explain the catalytic mechanism of action of yellow laccases.