An extracellular laccase-producing ascomycete was isolated from soil and identified as Paraconiothyrium variabile using rDNA sequence analysis. Typical laccase substrates including 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS), 2,6-dimethoxyphenol (DMP), and guaiacol were oxidized by the purified enzyme (designated as PvL). The molecular mass of PvL was 84 kDa and it showed a pl value of 4.2. The enzyme acted optimally at pH 4.8 and exhibited an optimum temperature of 50 degrees C. Using ABTS, PvL represented K(m) and V(max) of 203 mu M and 40 mu mol min(-1) mg(-1), respectively. After 24 h incubation at pH 4.8 and 4 degrees C, 80% of the initial activity of PvL remained. The enzyme was inhibited by Fe(2+), Hg(2+), and Mn(2+), but induced by Cu(2+). EDTA (10 mM), 1,4-dithiothreitol (OTT) (0.1 mM), and NaN(3) (10 mM) were found to completely inhibit PvL. Sixty-eight percent of Malachite green was decolorized by 4 U/mL of PvL after 15 min incubation at 30 degrees C. (C) 2010 Elsevier Ltd. All rights reserved.