Mechanisms for the oxidation of phenolic compounds by lignin peroxidase from Phanerochaete chrysosporium

Lignin peroxidase (LiP) from Phanerochaete chrysosporium has been implicated in the degradation of lignin and a variety of organopollutants. Mechanisms for the oxidation of phenolic compounds by LiP were investigated to better understand the involvement of LiP in the metabolism of phenolic compounds by the fungus.; It was found that phenolic compounds were as good a substrate for compound II as veratryl alcohol (VA). The results demonstrated that the inactivation of LiP during oxidation of phenolic compounds was mainly due to the accumulation of compound III, which was attributed to the inability of phenols or phenoxyl radicals to convert compound III to ferric enzyme (Chapter III).; Subsequent studies (Chapter IV) showed that phenol was oxidized indirectly in the presence of veratryl alcohol (VA) by LiP. The results obtained suggested that VA was first oxidized by LiP to VA cation radical (VA{dollar}sp{lcub}.+{rcub}{dollar}), which then oxidized phenol to phenoxyl radical while VA{dollar}sp{lcub}.+{rcub}{dollar} was reduced back to VA. LiP activity was lost as compound III accumulated since the VA{dollar}sp{lcub}.+{rcub}{dollar} was consumed by the oxidation of phenol. After all the phenol was oxidized, VA{dollar}sp{lcub}.+{rcub}{dollar} became available to revert compound III to an active ferric enzyme.; Pentachlorophenol (PCP) was also demonstrated to be oxidized through mediation via VA{dollar}sp{lcub}.+{rcub}{dollar} (Chapter V). However, unlike phenol oxidation in the presence of VA, compound II was observed since PCP reacted rather slowly with VA{dollar}sp{lcub}.+{rcub}{dollar} as compared to phenol. 2,3,5,6-Tetrachloro-p-benzoquinone was the major product during PCP oxidation both in the presence and absence of VA. An equivalent amount of inorganic chloride was formed by oxidative 4-dechlorination during PCP oxidation in the presence of VA.; To extrapolate these in vitro results to in vivo conditions, biodegradation of PCP by P. chrysosporium was demonstrated in soil (Chapter VI). This study demonstrated that P. chrysosporium degraded PCP efficiently and produced no harmful intermediates during degradation of PCP in soil, and that both PCP and pentachloroanisole, a PCP metabolite, were readily mineralized in soil.