Transformation of Halogen-, Alkyl-, and Alkoxy-Substituted Anilines by a Laccase of Trametes versicolor

Abstract

The laccase of the fungus Trametes versicolor was able to polymerize various halogen-, alkyl-, and alkoxy-substituted anilines, showing substrate specificity similar to that of horseradish peroxidase, whereas the laccase of Rhizoctonia praticola was active only with p -methoxyaniline. The substrate specificities of the enzymes were determined by using gas chromatography to measure the decrease in substrate concentration during incubation. With p -chloroaniline as the substrate, the peroxidase and the Trametes laccase showed maximum activity near pH 4.2. The transformation of this substrate gave rise to a number of oligomers, ranging from dimers to pentamers, as determined by mass spectrometry. The product profiles obtained by high-pressure liquid chromatography were similar for the two enzymes. A chemical reaction was observed between p -chloroaniline and an enzymatically formed dimer, resulting in the formation of a trimer. All three enzymes oxidized p -methoxyaniline to 2-amino-5- p -anisidinobenzoquinone di- p -methoxyphenylimine, but only the T. versicolor laccase and the peroxidase caused the formation of a pentamer (2,5-di- p -anisidinobenzoquinone di- p -methoxyphenylimine). Our results demonstrate that in addition to horseradish peroxidase, a T. versicolor laccase can also polymerize aniline derivatives.