Laccase on graphene oxide: Immobilization and use as a novel biocatalyst for phenol degradation

Laccases (E.C. 1.10.3.2, p-diphenyl: dioxygen oxidoreductase) belong to the so-called blue-copper family of oxidases[1], this enzyme has a high biotechnological interest as demonstrated by several studies reporting its use for green processes [2], such as bioremediation. Laccase from Myceliophthora thermophile (Novozym 51003) was immobilized on graphene oxide as a novel method of covalent immobilization by nucleophilic attack of amino groups of laccase to oxygen groups of the support. The enzyme loading on the support was about 94 mg/g under the optimum conditions (pH 4.5, 100 min). The effect of pH, temperature and organic solvent on immobilized enzyme activity was determined and compared with those of free enzyme. In general the immobilized enzyme was found to be stabilized compared to the free enzyme. The immobilized laccase was used for the oxidation of a mixture of six phenolic compounds (caffeic acid, ferulic acid, p-coumaric acid, protocatechuic acid, sinapic acid and vanillic acid) chosen among those present in olive mill wastewaters (OMWs) (scheme 1). Reaction yield observed for the oxidation of the examined phenolic compounds were different after 2 h (Table 1).