SUMMARY: A dikaryon of the basidiomycete growing in surface culture at 30 °C in the dark produced extracellular laccase (EC Little extracellular laccase was formed in the light or at 24 °C. The co-isogenic monokaryons from which the dikaryon was generated generally failed to produce laccase. The activity in the medium of the dikaryon accumulated until the glucose was consumed and then declined steadily. At its peak level of activity the enzyme accounted for about 3% of the extracellular protein. The enzyme was purified by DEAE-Sephacel chromatography. Substrate specificity and inhibitor studies showed the enzyme to be a typical fungal laccase. Electrophoresis of a purified enzyme preparation showed one major band accounting for 98% of the laccase proteins, and two minor bands with laccase activity. The major laccase protein was used to raise specific antibodies. After denaturation of the major laccase two immuno-reactive protein forms of 64 x 10 and 62 x 10 were produced, the former being convertible into the latter form. The intracellular extract contained one immuno-reactive protein of 72 x 10. The presence of laccase protein in the medium of various cultures was detected using Western blots. Accumulation of extracellular laccase protein only occurred in the dikaryon at 30 °C in the dark while the subsequent decrease in activity was not accompanied by a decrease in laccase protein.


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