Purification a laccase exhibiting dye decolorizing ability from an edible mushroom Russula virescens

A novel laccase was purified and characterized from an edible mushroom Russula virescens by using a protocol that comprised ammonium sulfate saturation, ion-exchange chromatography on diethylaminoethyl-cellulose, carboxymethyl-cellulose and quaternary amine-Sepharose, and finally gel filtration by fast protein liquid chromatography on Superdex 75. The laccase was a monomeric protein with a molecular mass of 69 kDa. Its N-terminal amino acid sequence was AIGPTAELVV which demonstrated partial sequence homology to those of previously published laccases. Six peptide sequences of the purified laccase were determined by liquid chromatography and linear ion trap quadrupole mass spectrometry. Its optimum pH and temperature were 2.2 and 60 °C, respectively. The laccase was inhibited by inhibitors and several metal ions including Cu²⁺ ions. The laccase degraded various phenolic compounds and the Km toward both 2,7-azinobis (3-ethylbenzothia-zolone-6-sulfonic acid) diammonium salt and dimethylphthalate was 0.1 mM. Moreover, the purified laccase decolorizes a large variety of dyes comprising laboratory dyes such as Bromothymol Blue, Eriochrome black T and Malachite Green and textile dyes such as Reactive Brilliant Blue and Reactive Blue R.