Abstract
The mechanism of wood degradation by the soft-rot deuteromycete, Graphium sp., was investigated. One-electron oxidation activity, assayed by ethylene generation from 2-keto-4-thiomethylbutyric acid (KTBA), and phenol oxidase activity were measured in intact cultures and in Sephadex G-50 fractions from the acetone-precipitated extracellular media, with glucose or wood as the carbon source for the cultures. Both the one-electron oxidation activity and the phenol oxidase activity were higher in wood cultures than in glucose cultures. Most of the phenol oxidase activity in wood cultures appeared to derive from laccase. Most of the ethylene generation from KTBA was attributed to hydroxyl radicals, produced by a lowmolecular-weight substance in the extracellular media. This substance was composed of peptides, carbohydrates, and Fe (II), and catalyzed redox reactions between O2 and unidentified electron donors, to produce hydroxyl radicals via H2O2. It is suggested that hydroxyl radicals may produce new phenolic substructures on the lignin polymer, making it susceptible to attack by laccase. Thus, both one-electron oxidation activity and laccase activity are important in wood degradation by Graphium sp.
