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Laccase isozymes have been identified in several fungi. We report the cloning of 4 laccase genes from the medicinal mushroom Agaricus brasiliensis. The lac1 gene contained a 1560-base pair (bp) open reading frame (ORF) encoding 520 amino acids that was interrupted with 14 introns in genomic DNA. The deduced amino acid sequence indicated a multicopper oxidase signature 1 and 2 multicopper oxidase signature 2. The lac2 gene contained a 1566-bp ORF encoding 522 amino acids that was interrupted with 13 introns in genomic DNA. A number of different nucleotides were observed in whole regions containing the substitution of amino acid residues (lac2a and lac2b). The partial DNA fragments of lac3 and lac4 genes were subcloned using the semi-random two-step polymerase chain reaction method. The lac3 and lac4 genes contained coding sequences with a 1575-bp ORF encoding 525 amino acids and a 1584-bp ORF encoding 528 amino acids, respectively. However, the whole complementary DNA fragment of both laccases could not be amplified with polymerase chain reaction against the complementary DNA library; therefore, introns were deduced based on the GT-AG rule and multiple alignment of laccases from other fungi, which showed high identity. All laccases from A. brasiliensis conserved the fungal laccase signature sequence and suggest 2 subfamilies according to the location of introns and phylogenetic analysis. The genes lac2 and lac4 had a high degree of identity, and the lac2a gene was located upstream of the lac4 gene.

The Royal Sun mushroom, the Himematsutake culinary-medicinal mushroom, Agaricus brasiliensis has several polyphenoloxidase activities in a broad sense. Here we report the partial purification of tyrosinase-type polyphenoloxidase (PPO). PPO is purified from A. brasiliensis without browning using a two-phase partitioning with Triton X-114 and ammonium sulfate fractionation. Partially denaturing SDS-PAGE (sodium dodecyl sulfate-polyacrylamide electrophoresis) staining with L-3,4-dihydroxyphenylalanine was performed and the indicated molecular sizes were approximately 70 kDa and 45 kDa. The purified enzyme is in its latent state and can be activated maximally in the presence of 1.6 mM sodium dodecyl sulfate (SDS). This enzyme catalyzes two distinct reactions, monophenolase and diphenolase activity, and the monophenolase activity showed a lag time typical of polyphenoloxidase. The K(m) value for 4-tert-butylcatechol was quite similar in the presence and absence of SDS, but the apparent V(max) value was increased 2.0-fold by SDS. Mimosine was a typical competitive inhibitor with K(i) values of 138.2 microM and 281.0 microM n the presence and absence of SDS, respectively.