Specifically, his current interests involve the biodegradation of the woody plant cell wall polymer, lignin, and aromatic pollutants by white-rot fungi. His lab is studying the structure and function of extracellular lignin-degrading peroxidases secreted by these organisms as well as intracellular enzymes involved in the degradation process. Genes encoding these enzymes have been cloned and a DNA transformation system and molecular genetic methods have been developed to study the mechanisms of these peroxidases, the regulation of their expression, and their role in lignin and pollutant degradation. These enzymes are secreted by the basidiomycetous fungus Phanerochaete chrysosporium .
Lignin peroxidase is able to oxidize nonphenolic lignin substrates to form aryl cation radicals.
We are using a variety of polymeric substrates including cytochrome c to model the lignin peroxidase oxidation of polymeric lignin. In contrast to lignin peroxidase, manganese peroxidase oxidizes Mn II to Mn III , which is then chelated by various organic acids such as oxalate and diffuses away from the enzyme to oxidize the terminal lignin substrate. Biochemical, spectroscopic, and kinetic methods are being used to further elucidate the unique structure, mechanism, and specificity of each of these peroxidases. In addition, we are studying the role of these and other enzymes in the degradation of aromatic pollutants, including chlorophenols, chlorinated dioxins, chlorophenoxyacetic acids, and nitroaromatics. Several intracellular enzymes involved in these degradative processes, including a quinone reductase and aromatic nitro reductase, have also been characterized.