Structure of the

Chicago Sky Blue (Figure 2) is a disazo dye used extensively in dyeing cotton and cellulosic fiber material. It is often

*One unit (U) of enzyme activity is defined as the amount of enzyme causing a change in absorbance of 1.0 min 1 at room temperature (Bourbonnais and Paice 1990).

Figure 1 Decolorization of effluent by P. cinnabarinus.

incorporated into inks, and used for dyeing of leather and paper. It belongs to the largest class of commercially produced water-soluble dyes that are characterized by up to three azo linkages which link phenyl and naphthyl groups containing combinations of functional groups (sulfonic acid, sodium salt; amino; chloro; hydroxyl; methyl and nitro) on the rings.

Decolorization and degradation of azo dyes have been demonstrated with P. chrysosporium (Cripps et al. 1990; Ollikka et al. 1993; Pasti-Grigsby et al. 1992; Paszczynski et al. 1991; 1992; Spadaro et al. 1992). A lignin peroxidase of this organism catalyses the decolorization of azo, hetero-cyclic, triphenylmethane, and polymeric dyes (Ollikka et al. 1993).

Much less is known about the role of laccases in the decolorization of synthetic dyes, although several wood-rotting fungi produce laccase as well as peroxidases and have been shown to decolorize a range of structurally different dyes (Knapp et al. 1995). A mechanism for degradation of phenolic azo dyes by laccase from Pyricularia oryzae (Chivukula and Renganathan 1995) is similar to the one proposed for degradation of phenolic azo dyes by a lignin peroxidase (Chivukula et al. 1995). In the latter case formation of novel sulfophenyl hydroperoxides was postulated and the elimination of the azo linkage as molecular nitrogen. However, in the case of laccase, electron-rich

S03Na SO-jNa

Figure 2 Structural formula of Chicago sky blue (CSB).

S03Na SO-jNa

Figure 2 Structural formula of Chicago sky blue (CSB).

phenolic rings adjacent to the azo linkage appeared necessary for oxidation and phenoxy radical formation. Mass spectral (MS) and electrospray ionization (EI)-MS analyses confirmed the release of azo linkages as molecular nitrogen. This prevented aromatic amine formation.

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