PATHWAYS OF PRODUCTION OF FENTON REAGENT BY WOOD-ROTTING FUNGI

Many forms of Fe(II) react with H2O2 to generate hydroxyl radicals (Fe nton reaction). There is evidence that hydroxyl radicals are important in brown-rot, while they can be formed by secondary reactions during lignin breakdown by white-rot fungi. Their involvement in cellulose br eakdown creates a range of oxidized sugars. The two reactants of Fento n's reagent can be generated by Fe(II) autoxidation, or by superoxide in reaction with Fe(III). A rapid autoxidation is not possible for com plexes with a high Fe(III)/Fe(II) redox potential. Turning to specific pathways for formation of Fenton's reagent, decomposition of Fe(III)- oxalate is probably solely a photochemical process. Lignin peroxidases can act indirectly as a source of superoxide, either by reactions tha t lead to a peroxyradical, or by 1-electron oxidation of an aliphatic compound creating a strong reductant. Cellobiose dehydrogenase can pro vide a direct enzymic source for Fenton's reagent (S.M. Kremer and P.M . Wood (1992) Eur. J. Biochem. 208, 807-814). In the experiments as pu blished, hydroxyl radical production was limited by the slow interacti on of cellobiose dehydrogenase with O2. This limitation can be removed by the presence of an iron complex with an autoxidizable Fe(II) state . The successful use of Fenton's reagent by a living organism requires a spatial separation between initiating enzyme(s) and the site of pro duction of hydroxyl radicals. The mobility of the extra electron on Fe (II) by intermolecular transfer may be important for achieving this se paration.