Purification of a new manganese peroxidase of the white-rot fungus Irpex lacteus, and degradation of polycyclic aromatic hydrocarbons by the enzyme

The white-rot fungus Irpex lacteus has been reported to be an efficient degrader of polycyclic aromatic hydrocarbons, polychlorinated biphenyls and pentachlorophenol. The fungus produces ligninolytic enzymes laccase, lignin peroxidase and manganese peroxidase (MnP), the latter being the major one produced. MnP was purified using anion exchange and size exclusion chromatography. SDS–PAGE showed the purified MnP to be a monomeric protein of 37 kDa (37.5 kDa using MALDI-TOF) with an isoelectric point at 3.55. The pH optimum was relatively broad, from 4.0 to 7.0 with a peak at pH 5.5. Kinetic constants Km were 8 μM for H2O2 and 12 or 31 μM for Mn2+ depending on the substrate. The enzyme did not perform oxidation in the absence of H2O2 or Mn2+. MnP was active at 5–70 °C with an optimum between 50–60 °C. At temperatures above 65 °C the enzyme rapidly lost activity. Degradation of four representatives of PAHs (phenanthrene, anthracene, fluoranthene, and pyrene) was tested and the enzyme showed the ability to degrade them in vitro. Major degradation products of anthracene were identified. The results confirm the role of MnP in PAH degradation by I. lacteus, including cleavage of the aromatic ring.