A novel laccase from the edible mushroom Clitocybe maxima was purified and characterized. The purification protocol involved ammonium sulfate saturation, ion-exchange chromatography on DEAE-cellulose, SP-Sepharose, and Q-Sepharose, and gel filtration by fast protein liquid chromatography on Superdex 75. It was a monomeric protein with a molecular mass of 62 kDa as estimated by SOS-PAGE. Its N-terminal amino acid sequence was DIGPVTPLAI, which exhibited partial sequence homology to those of published mushroom laccases. Its optimum pH was 3.0 and its optimum temperature was 60 degrees C. It manifested degrading activity towards a variety of phenolic compounds. The most sensitive substrate for the enzyme was 2,7'-azinobis[3-ethylbenzothiazolone-6-sulfonic acid]diammonium salt (ABTS), with a K(m) of 61.7 mu M at pH 3.0 and 37 degrees C. The ranking of degradation activity toward phenolic substrates was ABTS > hydroquinone > N,N-dimethyl-1,4-phenylenediamine > pyrogallol > catechol > 2-methylcatechol. The laccase showed antiproliferative activity against Hep G2 and MCF-7 tumor cells with IC(50) of 12.3 mu M and 3.0 mu M, respectively. It also lowered the activity of human immunodeficiency virus-1 (HIV-1) reverse transcriptase with an IC(50) of 14.4 mu M. (C) 2009 Elsevier Ltd. All rights reserved.