Relationship between mineralization of synthetic lignins and the generation of hydroxyl radicals by laccase and a low molecular weight substance produced by Petriellidium fusoideum

A new ligninolytic fungal strain was isolated from the Peruvian Amazon forest. Its enzymatic profile revealed a laccase as the only enzyme related to lignin metabolism. Its partial inhibition with thioglycolate also reduces mineralization. Production of hydroxyl radicals was detected from the first day of incubation. Their inhibition involves a substantial decrease in the mineralization of synthetic lignins. Besides this, the fungus produced a protein-free low molecular weight substance “LMW-S” (about 1.6 kDa) containing 0.1% Fe2+. To elucidate the cooperation between laccase and the LMW-S in producing the hydroxyl radicals (radical dotOH) excreted by this fungus in lignin degradation, different systems composed of partially purified enzyme, LMW-S, and some substrates recognised by the laccase were assayed. A hypothetical mechanism is proposed for the generation of radical dotOH radical in this system, in an attempt to explain its participation in the mineralization produced by the fungus.