A laccase with a novel N-terminal sequence, a molecular mass of 63kDa, and inhibitory activity toward HIV-1 reverse transcriptase (IC(50)=9.5microM) was isolated from dried fruiting bodies of the monkey head mushroom Hericium erinaceum. A chromatographic procedure involving ion exchange chromatography on DEAE-cellulose, CM-cellulose, and Q-Sepharose and fast protein liquid chromatography-gel filtration on Superdex 75 was employed. The laccase was adsorbed on DEAE-cellulose and Q-Sepharose but unadsorbed on CM-cellulose. High activity of the enzyme was observed at pH 3-5 and at 50-80 degrees C. Its activity was completely abolished at pH 8 and 9 and after boiling for 10min. A temperature of 50 degrees C and a pH of 5.0 were optimal for its activity.