Purification and characterization of laccase from the white-rot fungus Daedalea quercina and decolorization of synthetic dyes by the enzyme

Abstract

The white-rot fungus Daedalea quercina produced the ligninolytic enzymes laccase and Mn-dependent peroxidase. Laccase was purified using anionexchange and size-exclusion chromatographies. SDS-PAGE showed the purified laccase to be a monomeric protein of 69 kDa (71 kDa using gel filtration) with an isoelectric point near 3.0. The optimum pH for activity was bellow 2.0 for 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (Km=38 μM), 4.0 for 2,6-dimethoxyphenol (Km=48 μM), 4.5 for guaiacol (Km=93 μM) and 7.0 for syringaldazine (K m=131 μM). The temperature optimum was between 60 and 70°C depending on the pH and buffer used. The enzyme was stable up to 45°C, and stability was higher at alkaline pH. Enzyme activity was increased by the addition of Cu2+ and inhibited by Mn2+, sodium azide, dithiothreitol, and cysteine. Laccase from Daedalea quercina was able to decolorize the synthetic dyes Chicago sky blue, poly B-411, remazol brilliant blue R, trypan blue and reactive blue 2.