1996 Fiscal Year Final Research Report Summary
The involvement of extracellular substances for the generation of hydroxyl radical during wood degradation by white-rot fungi
| Project/Area Number |
07806045
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
生物資源科学
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| Research Institution | KINKI UNIVERSITY |
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Principal Investigator |
TANAKA Hiromi KINKI UNIVERSITY,FACULTY OF AGRICULTURE,ASSOCIATE PROFESSOR, 農学部, 助教授 (30140338)
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| Project Period (FY) |
1995 – 1996
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| Keywords | White-rot fungi / Hydroxyl radical / One-electron oxidation / Wood degradation / Lignin-degrading fungi / Ferrous iron / Ferric iron / Reduction |
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| Research Abstract |
In the present research, we examined the possible roles of one-electron oxidation activity by phenol oxidases and hydroxyl radicals produced by extracellular low molecular weight substances in wood degradation by white-rot fungi.
We demonstrated hydroxyl radical was produced during wood degradation by four white-rot fungi. The rate of degradation of wood by P.chrysosporium correlated with hydroxyl radical generation as well as ethylene generation by fractions of low molecular weight. The same tendency was observed in C.versicolor. The assay for phenol oxidase activity proved that P.chrysosporium produced manganese peroxidase dominantly in wood cultures and produced manganese peroxidase and peroxidase in the very early stage of incubation. C.versicolor produced mainly peroxidase and laccase in wood cultures and retained almost same level of activity throughout incubation. Therefore, the substrate specificity and the constituent of phenol oxidizing enzymes of the fungus were very different from another. Consequently, the rate of degradation of wood by white-rot fungi was not dependent upon the activities of oxidants such as phenol oxidases.
Immunogold-TEM using polyclonal antibodies raised against Tyromyces palustris extracellular low molecular weight substance demonstrated the diffusion of the substance from the fungal hyphae within the cell lumen to the S_2 cell wall.
In conclusion, hydroxyl radicals attack the wood component and cause the initial step of degradation, which is destruction of the rigid structure by cleavage of covalent bonds. Further, HO・may achieve other structural changes to facilitate the subsequent enzymatic breakdown of the fragments which were degraded by oxidative enzymes secreted by white-rot fungi. White-rot fungi produce oxidative enzymes, capable of completing the breakdown of wood.
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