Redox chemistry in laccase-catalyzed oxidation of N-hydroxy compounds

1-Hydroxybenzotriazole, violuric acid, and N-hydroxyacetanilide are three N -OH compounds capable of mediating a range of laccase-catalyzed biotransfor mations, such as paper pulp delignification and degradation of polycyclic h ydrocarbons. The mechanism of their enzymatic oxidation was studied with se ven fungal laccases. The oxidation had a bell-shaped pH-activity profile wi th an optimal pH ranging from 4 to 7. The oxidation rate was found to be de pendent on the redox potential difference between the N-OH substrate and la ccase. a laccase with a higher redox potential or an N-OH compound with a l ower redox potential tended to have a higher oxidation rate. Similar to the enzymatic oxidation of phenols, phenoxazines, phenothiazines, and other re dox-active compounds, an "outer-sphere" type of single-electron transfer fr om the substrate to laccase and proton release are speculated to be involve d in the rate-limiting step for N-OH oxidation.