Abstract Laccases could prevent fabrics and garments from re-deposition of dyes during washing and finishing processes by degrading the solubilized dye. However, laccase action must be restricted to solubilized dye molecules thereby avoiding decolorization of fabrics. Chemical modification of enzymes can provide a powerful tool to change the adsorption behaviour of enzymes on water insoluble polymers. Polyethyl- ene glycol (PEG) was covalently attached onto a laccase from Trametes hirsuta. Different molecu- lar weights of the synthetic polymer were tested in terms of adsorption behaviour and retained laccase activity. Covalent attachment of PEG onto the laccase resulted in enhanced enzyme stability while with increasing molecular weight of attached PEG the substrate affinity for the lac- case conjugate decreased. The activity of the modified laccases on fibre bound dye was drasti- cally reduced decreasing the adsorption of the enzyme on various fabrics. Compared to the 5 kDa PEG laccase conjugate (K/S value 47.60) the K/S value decreased much more (47.96–46.35) after the treatment of dyed cotton fabrics with native laccase. Keywords Laccase Æ Polyethylene glycol Æ Dye-degrading Æ Enzyme modification Æ Trametes hirsuta Introduction Indigo and Remazol Briliant Blue R are widely applied industrial dyes. Previous studies have shown the degradation of different commercial dyes using crude and purified laccases from Trametes hirsuta (Campos et al. 2001; Rodriguez Couto et al. 2005). Besides the reduction of environmental pollution (Nyanhongo et al. 2002; Sorares et al. 2001), enzymatic decolourisation of dyeing effluents has been shown to enable re-use of the treated water in dyeing (Abadulla et al. 2000). Furthermore, laccase has been introduced for indigo oxidation on denim garments (Galante and Formantici 2003), so called ‘biobleaching’ and removal of extensive dye after dyeing. Re-deposition of Indigo dye during enzymatic stone-washing of denim garments with cellulases seems to be a major problem (Cavaco-Paulo 1998; Andreaus and Campos 2001). Similar effects occur during the washing process in the house- hold laundry of coloured garments. Laccases M. Schroeder Æ S. Heumann Æ G. M. Guebitz (&) Department of Environmental Biotechnology, Graz University of Technology, Petersgasse 12, A-8010 Graz, Austria e-mail: guebitz@tugraz.at C. J. S. M. Silva Æ A. Cavaco-Paulo Textile Engineering Department, University of Minho, 4800-058 Guimara ˜ es, Portugal Biotechnol Lett (2006) 28:741–747 DOI 10.1007/s10529-006-9052-4 123 ORIGINAL PAPER Specificities of a chemically modified laccase from Trametes hirsuta on soluble and cellulose-bound substrates M. Schroeder Æ S. Heumann Æ C. J. S. M. Silva Æ A. Cavaco-Paulo Æ G. M. Guebitz Received: 15 November 2005 / Accepted: 9 January 2006 / Published online: 30 May 2006 Ó Springer Science+Business Media B.V. 2006