Indigo degradation with purified laccases from Trametes hirsuta and Sclerotium rolfsii

The degradation of the textile dye indigo with purified laccases from the fungi Trametes hirsuta (THL1 and THL2) and Sclerotium rolfsii (SRL1) was studied. All laccases were able to oxidize indigo yielding isatin (indole-2,3-dione), which was further decomposed to anthranilic acid (2-aminobenzoic acid). Based on the oxygen consumption rate of the laccases during indigo degradation, a potential mechanism for the oxidation of indigo involving the step-wise abstraction of four electrons from indigo by the enzyme was suggested. Comparing the effect of the known redox-mediators acetosyringone, 1-hydroxybenzotriazole (HOBT) and 4-hydroxybenzenesulfonic acid (PHBS) on laccase-catalyzed degradation of indigo, we found a maximum of about 30% increase in the oxidation rate of indigo with SRL1 and acetosyringone. The particle size of indigo agglomerates after laccase treatment was influenced by the origin of the laccase preparation and by the incubation time. Diameter distributions were found to have one maximum and compared to the indigo particle size distribution of the control, for all laccases, the indigo agglomerates seemed to have shifted to smaller diameters. Bleaching of fabrics by the laccases (based on K/S values) correlated with the release of indigo degradation products. (C) 2001 Elsevier Science BY. All rights reserved

An acid-stable laccase from sclerotium rolfsii with potential for wool dye decolourization

The plant pathogen basidiomycete S. rolfsii secretes two laccases (SRL1 and SRL2) with molecular weights of 55 and 86 kDa, respectively. Laccase production was shown to be inducible by the addition of 2,5-xylidine to the cultural media. After treatment with a combination of chitinase and -1,3-glucanase, two different laccases were isolated from the sclerotia depending on the stage of sclerotia development. The more prominent laccase, SRL1, was purified and found to decolourize the industrially important wool azo dye Diamond Black PV 200 without the addition of redox mediators. The enzyme (pI 5.2) was active in the acidic pH range, showing an optimal activity at pH 2.4, with ABTS as substrate. The optimum temperature for activity was determined to be 62 ◦C. Enzyme stability studies revealed that SRL1 was notably stable at 18 ◦C and pH 4.5, retaining almost full activity after a week. Oxidation of tyrosine was not detectable under the reaction conditions but the enzyme did oxidize a variety of the usual laccase substrates. SRL1 was strongly inhibited by sodium azide and fluoride. Dye solutions decolourized with the immobilized laccase were successfully used for redyeing.(undefined