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thermostable laccase was isolated from a tropical white-rot fungus Polyporus sp. which produced as high as 69,738 units of laccase l in an optimized medium containing 20 g of malt extract l, 2 g of yeast extract l, 1.5 mM CuSO. The laccase was purified to electrophoretic purity with a final purification of 44.70-fold and a recovery yield of 21.04%. The purified laccase was shown to be a monomeric enzyme with a molecular mass of 60 kDa. The optimum temperature and pH value of the laccase were 75°C and pH 4.0, respectively, for 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonate) (ABTS). The Michaelis-Menten constant ( K) of the laccase was 18 μM for ABTS substrate. The laccase was stable at pH values between 5.5 and 7.5. About 80% of the initial enzyme activity was retained after incubation of the laccase at 70°C for 2 h, indicating that the laccase was intrinsically highly thermostable and with valuable potential applications. The laccase activity was promoted by 4.0 mM of Mg, Mn, Zn and Ca, while inhibited by 4.0 mM of Co, Al, Cu, and Fe, showing different profiles of metal ion effects. [ABSTRACT FROM AUTHOR]