Immobilisation of tyrosinase on siliceous cellular foams affording highly effective and stable biocatalysts

Tyrosinase from Agaricus bisporus was immobilised covalently on mesostructured siliceous foam (MCF) and three mesoporous silicas of SBA-15 type of different pore sizes, regarded as the reference, to reveal that MCF was the superior enzyme support. All the carriers were functionalised using 3-aminopropyltrimethoxysilane and the enzyme was attached covalently via glutaraldehyde or by simple adsorption and it was also cross-linked with glutaraldehyde in selected samples. The experiments indicated that only tyrosinase attached covalently was highly active and that postimmobilisation cross-linking slightly reduced its activity with no improvement in stability. MCFbound tyrosinase was the best biocatalyst with monophenolase and diphenolase activities of 3627 U mL^-1 and 53040 U mL^-1 of carrier sediment, respectively. Inactivation studies at 55°C showed that MCF-bound tyrosinase was 20 times more stable than the native enzyme, whereas for typical SBA-15 it was only 12 times. A comparative study with other, non-siliceous enzyme supports indicated that aminated MCF appeared to be the carrier of choice for the covalent attachment of tyrosinase.