White rot fungi are the most significant lignin degraders among the wood inhabiting microorganisms. They degrade lignin by extracellular oxidative enzymes. The ligninolytic enzymes also oxidize various environmental pollutants such as polycyclic aromatic hydrocarbons, chlorophenols, and aromatic dyes. The most ubiquitous ligninolytic enzymes produced by these fungi are lignin peroxidases (LP), manganese peroxidases (MnP), and laccases (phenol oxidases). The peroxidases are heme-containing enzymes having typical catalytic cycles, which are characteristic of other peroxidases as well. One molecule of hydrogen peroxide oxidizes the resting (ferric) enzyme withdrawing two electrons. Then the peroxidase is reduced back in two steps of one electron oxidation in the presence of appropriate reducing substrate. The range of the reducing substrates of the two peroxidases is very different due to their altered substrate binding sites. LP is able to oxidize various aromatic compounds, while MnP oxidizes almost exclusively Mn(II) to Mn(III), which then degrades phenolic compounds. Laccases are copper-containing oxidases. They reduce molecular oxygen to water and oxidize phenolic compounds. In this paper, the mechanism of pollutant oxidation by ligninolytic enzymes is discussed giving an overview on the recent results of enzyme kinetics and structure. (C) 2000 Elsevier Science Ltd.
All Science Journal Classification (ASJC) codes
- Waste Management and Disposal