a b s t r a c tAgaricus bisporous tyrosinase was immobilized on commercial available epoxy-resin Eupergit Ò C250L and then coated by the Layer-by-Layer method (LbL). The two novel heterogeneous biocatalysts were characterized for their morphology, pH and storage stability, kinetic properties (K m , V max , V max /K m ) and reusability. These biocatalysts were used for the efficient and selective synthesis of bioactive catechols under mild and environmental friendly experimental conditions. Ascorbic acid was added in the reaction medium to inhibit the formation of ortho-quinones, thus avoiding the known enzyme suicide inactivation process. Catechols were obtained mostly in quantitative yields and conversion of substrate. Tyrosinase immobilized on Eupergit Ò C250L and coated by the LbL method showed better catalytic activities, higher pH and storage stability, and reusability with respect to immobilized uncoated tyrosinase. Since chemical procedures to synthesize catechols are often expensive and with high environmental impact, the use of immobilized tyrosinase represents an efficient alternative for the preparation of this family of bioactive compounds.

Horseradish peroxidase (HRP) was chemically immobilised onto alumina particles and coated by polyelectrolytes layers, using the layer-by-layer technique. The reactivity of the immobilised enzyme was studied in the oxidative functionalisation of softwood milled wood and residual kraft lignins and found higher than the free enzyme. In order to investigate the chemical modifications in the lignin structure, quantitative (31)P NMR was used. The immobilised HRP showed a higher reactivity with respect to the native enzyme yielding extensive depolymerisation of lignin.

Commercial and extracted mushroom tyrosinases were supported on Eupergit C 250 L and protected by a coating of oppositely charged polyelectrolytes by means of the layer‐by‐layer technique. The kinetic parameters (Km, Vmax, and Vmax/Km) of these novel biocatalysts in both organic and aqueous media were evaluated, showing tyrosinase to be more reactive in organic solvent than in buffer solution. Heterogeneous tyrosinase systems were used for the oxidation of a large group of phenol derivatives to the corresponding catechols. Different enzyme reactivities were found depending on the substrate structure. The catalyst activity was retained for successive runs. Catechols are difficult to synthesize through traditional chemical methods under environmentally friendly conditions; the use of immobilized tyrosinase opens a novel synthetic alternative to this interesting biologically active family of substances.

Horseradish peroxidase (HRP) was immobilised on Eupergit C 250 L resin coated with poly‐electrolytes, or by entrapment inside pre‐formed layer‐by‐layer (LbL) micro‐capsules of poly‐electrolytes. In these systems, namely HRP/E‐LbL, HRPm/LbL and HRPm/LbLp, the native enzyme retained its catalytic activity. Immobilised HRP showed a significant activity in the oxidation of selected azo, quinoline and fluorone dyes with H2O2 as the primary oxidant under mild experimental conditions, and HRPm/LbL was the best catalyst. A comparison between the catalytic efficiency of different redox mediators for HRP activity was made by using 1‐hydroxybenzotriazole (HOBt), violuric acid (VLA) and veratrylic alcohol (VA). As a general trend, azo dyes were degraded in higher yields, and HOBt was the best mediator for the oxidation. The degradation yield increased on increasing the reaction time and reached the highest value after 12 h, which is comparable with that observed for native HRP. Notably, HRPm/LbL retained its catalytic activity for more runs.

Abstract3,4‐Dihydroxyphenylalanine (DOPA)‐containing peptides and proteins provide attractive design paradigms for pharmaceutical applications and engineering of synthetic polymers. An efficient and selective route to DOPA peptides by oxidation of L‐tyrosine derivatives with tyrosinase is reported. The efficiency of the procedure was tested by using successively recycled tyrosinase immobilized on Eupergit®C250L and coated with polyelectrolytes by the layer‐by‐layer method.