Degradation of Phenolic Compounds and Ring Cleavage of Catechol by Phanerochaete chrysosporium.
POL-88, a mutant of the white-rot fungus Phanerochaete chrysosporium, was selected for diminished phenol-oxidizing enzyme activity. A wide variety of phenolic compounds were degraded by ligninolytic cultures of this mutant. With several o-diphenolic substrates, degradation intermediates were produced that had UV spectra consistent with muconic acids. Extensive spectrophotometric and polarographic assays failed to detect classical ring-cleaving dioxygenases in cell homogenates or in extracts from ligninolytic cultures. Even so, a sensitive carrier-trapping assay showed that intact cultures degraded [U-C]catechol to [C]muconic acid, establishing the presence of a system capable of 1,2-intradiol fission. Significant accumulation of [C]muconic acid into carrier occurred only when evolution of CO(2) from [C]catechol was inhibited by treating cultures with excess nutrient nitrogen (e.g., l-glutamic acid) or with cycloheximide. l-Glutamic acid is known from past work to repress the ligninolytic system in P. chrysosporium and to mimic the effect of cycloheximide. The results here indicate, therefore, that the enzyme system responsible for degrading ring-cleavage products to CO(2) turns over faster than does the system responsible for ring cleavage.
Leatham
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Forest Products Laboratory, Forest Service, U.S. Department of Agriculture, Madison, Wisconsin 53705, and Gray Freshwater Biological Institute and Department of Microbiology, University of Minnesota, Navarre, Minnesota 55392.
Crawford
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RL
Kirk
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TK