Purification and characterization of a novel trimeric and thermotolerant laccase produced from the ascomycete Scytalidium thermophilum strain

A novel laccase from the thermophilic ascomycete fungus Scytalidium thermophilum strain was purified and their biochemical properties were determined. The laccase was purified 8-fold with a specific activity of 139.4 U/mg. This laccase was found to be a homotrimeric protein (subunit molecular-weight of about 28 kDa) with 82 kDa as a total molecular-weight. Its optimum activity pH varied and was substrate dependent. Indeed, it was 5.0 for ABTS and DMP and 6.0 for guaiacol and hydroquinone. Its optimum temperature was 80 °C using DMP as substrate. The enzyme retained 50% of its activity after 120 min of incubation at 70 °C. Under standard assay conditions, laccase Km values were 0.36 mM and 0.26 mM towards 2,6-DMP and ABTS, respectively. It has shown a degrading activity towards a variety of phenolic compounds. The laccase was inhibited by NaN3, DTT, SDS and p-coumarate but not by EDTA, l-Cys, NaF and NaBr. Furthermore, this laccase was stable in the presence of some metal ions.