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Verwertbare Ergebnisse
Basidiomycetous fungi which cause white-rot in wood are the most efficient lignin degraders in nature. These fungi produce lignin-modifying enzymes such as laccase, lignin peroxidases and manganese peroxidases in varying combinations. Laccase (benzenediol:oxygen oxiodore-ductase) is a copper-containing oxidase which utilises molecular oxygen as oxidant and normally oxidises e.g. phenolic rings to phenoxy radicals. Although the exact role of the laccase in lignin biodegradation is not known, these enzymes may have applications e.g. in pulp and paper industry and in removal of environmental pollutants from soil and water. A laccase-mediator system for pulp bleaching has recently been published.
The objective of this project was to clarify the structure and function of laccase and oxidase enzymes produced by different basidiomycetous fungi. The efficiency and capacity of these enzymes to oxidise aromatic compounds were investigated. Joint research activities of Institute of Biochemistry and Physiology of Micro-organisms (Pushchino, Russia), University of Helsinki (Helsinki, Finland) and King's College London (UK) were aimed to conduct studies on laccases from six ligninolytic fungi (Panus tigrinus, Coriolus versicolor, Phlebia radiata, Phlebia tremellosa, Agaricus bisporus and Armillaria mellea). Analytical and spectroscopic equipments and know-how of these laboratories were available for mutual benefits of the project realisation. The project was carried out according to the plan i.e. experiment, working visits to utilise equipment and other facilities, and meetings were realised in accordance with the time schedule and finished during the project duration.
The most important result of the project was the unexpected finding of a new form of fungal laccase which was called "yellow" laccase due to the typical colour, in contrast to normal "blue" laccase. A hypothesis was formulated to explain this phenomenon. The main idea of this hypothesis is "reversible reduction" of the active sites of the yellow laccases; this reduction is caused by modification of originally blue laccases to its yellow forms by reactive products of lignin degradation. This modification enhances oxidation capability of the enzymes. Thus the yellow laccases were able to oxidise highly persistent non-phenolic compounds. This ability resembles recently described blue laccase/electron-transfer mediator pairs, and moreover, this phenomenon could explain the involvement of laccase in lignin degradation under natural conditions, i.e. when the fungus grows on straw or wood.
Other results can be summarised as follows: isolation and characterisation of blue, four-copper atom containing laccase from Phlebia radiata, earlier reported to produce yellow two-copper containing laccase; determination of laccase nature of yellow oxidase -1 from Panus tigrinus, assumed before to be a new unusual fungal oxidase; determination of conditions of cultivation of fungi to result in formation of yellow forms of laccases; purification and characterisation of 14 enzymes, including blue and yellow pairs of laccases from five different fungi, laccase isozymes from two fungi and two unusual oxidases from Panus tigrinus.
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