Melanin produced by Hypoxylon archeri, a companion fungus of Tremella fuciformis, was purified from the submerged culture medium and designated as HM. Ultraviolet-visible and FTIR spectra of the purified HM showed significant similarities with those of the synthesized melanin derived from tyrosine. Thus, the HM melanin was identified to be derived from the precursor molecule of tyrosine or dihydroxyphenylalanine (DOPA). The antioxidant activity of HM melanin, synthetic melanin and vitamin C were compared by inhibition of the oxidation of 5-thio-2-nitrobenzoic acid (TNB) caused by hypochlorous acid (HOCl) and hydrogen peroxide (H(2)O(2)). The HM melanin is likely to be more efficient eliminating oxygen free radicals generated by H(2)O(2) than by HOCl. At a concentration of 100 mg x l(-1), the HM melanin protected 80.95% of TNB oxidation by H(2)O(2), slightly higher than the synthetic melanin. Inhibition curves as a function of time also revealed the HM melanin was a more efficient inhibitor of H(2)O(2) oxidation with an average TNB (TNB(acr)) consumption rate of 0.0553 mmol l(-1 ) x min(-1 )during the inhibition phase. Therefore, HM melanin is an efficient scavenger of peroxide free radicals.
Hydrophobins are a family of small, moderately hydrophobic proteins with eight cysteine residues arranged in a conserved pattern. A full-length cDNA, designated Po.hyd, corresponding to a hydrophobin gene of Pleurotus ostreatus was obtained in our previous work. The Po.hyd gene contains a 333 bp open reading frame (ORF), which is interrupted by two typical classI introns. There was no consensus signal for a polyA tail detected in the 3'untranslated region. However, an analogous T- or TG-rich motif was observed that probably influence the formation of the mRNA 3' end. We assign the putative Po.HYD protein to the classI hydrophobins since its sequence arrangement and hydropathy pattern has a high consensus to other known class I hydrophobins. Northern analysis showed that the Po.hyd gene was abundantly expressed throughout the fruiting process (from primordium to mature fruiting body) but silenced during vegetative growth of the mycelium. Southern blot analysis showed Po.hyd to be a single copy gene in the genome of dikaryotic strain likely to locate at the same locus within the two parental genomes.
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