Kinetics of the enzymatic decolorization of textile dyes by laccase from Cerrena unicolor

This study deals with the laccase-catalyzed decolorization of azo and anthraquinone dyes. Both purified laccase (Lacc I and Lacc II) as well as the crude enzyme from the white-rot fungus Cerrena unicolor were used to convert the dyes at pH 3.5 (optimum of laccase activity) in aqueous solution. Biotransformation of the dyes was followed spectrophotometrically and confirmed by high performance liquid chromatography (HPLC). The results indicate that the decolorization mechanism follows Michaelis–Menten kinetic and that the initial rate of decolorization depends both on the structure of the dye and on the dye concentration. The saturation constants (Km) of purified laccase isoforms (Lacc I, II) differ to some extend indicating different substrate affinities. Surprisingly, one recalcitrant azo dye (AR 27) was decolorized merely by purified laccase in the absence of any redox mediator.