The tolerance of lignin peroxidase and manganese-dependent peroxidase to miscible solvents and the in vitro oxidation of anthracene in solvent: Water mixtures

Lignin peroxidase (LiP) and manganese-dependent peroxidase (MnP) titers in extracellular fluids of five-day-old Bjerkandera sp. strain BOS55 cultures and semipurified preparations from Phanerochaete chrysosporium were evaluated for their tolerance to miscible solvents. MnP assayed with 2,6-dimethoxyphenol (DMP) was found to retain 20% of its normal activity in the presence of 45-58% v/v acetone, 31-34% v/v ethanol, and 29% 2-propanol. LiP assayed with veratryl alcohol (VA) was about 2-3 times less tolerant to solvents compared to MnP. Methanol and 2-methoxyethanol were extremely inhibitory to LiP. The subtoxic concentrations of acetone were sufficient to remarkably increase the solubility of the model apolar pollutant, anthracene. Each 10% increment in the solvent concentration could be correlated to a 6.4-fold increase in the soluble anthracene concentration. When the peroxidases were incubated in vitro with anthracene as a substrate, acetone was essential for the elimination of anthracene and concomitant formation of anthraquinone. We observed for the first time a H₂O₂-enhanced oxidation of a polycyclic aromatic hydrocarbon, anthracene, by MnP when enough acetone was used (40% v/v). At acetone concentrations ranging from 5-60%, MnP was also able to oxidize anthracene in the absence of exogenous H₂O₂ additions but to a lesser extent. The optimum acetone concentration for the LiP-mediated oxidation of anthracene was 10% v/v. The in vitro oxidation rates with semipurified LiP (65 nmol VA min^-1 ml^-1) and MnP (33 nmol DMP min^-1 ml^-1) at the optimal solvent concentration was 4.3 and 4.0 mg anthracene l^-1 d^-1, respectively. The rate of anthracene conversion by LiP was similar to the anthracene dissolution rate in 10% acetone. In contrast, the conversion by MnP was estimated to be several orders of magnitude slower than the dissolution kinetics in 40% acetone.