The direct involvement of manganese peroxidase (MnP) in the mineralization of natural and xenobiotic compounds was evaluated. A broad spectrum of aromatic substances were partially mineralized by the MnP system of the white rot fungus Nematoloma frowardii. The cell-free MnP system partially converted several aromatic compounds, including [U-C]pentachlorophenol ([U-C]PCP), [U-C]catechol, [U-C]tyrosine, [U-C]tryptophan, [4,5,9,10-C]pyrene, and [ring U-C]2-amino-4,6-dinitrotoluene ([C]2-AmDNT), to CO(2). Mineralization was dependent on the ratio of MnP activity to concentration of reduced glutathione (thiol-mediated oxidation), a finding which was demonstrated by using [C]2-AmDNT as an example. At [C]2-AmDNT concentrations ranging from 2 to 120 muM, the amount of released CO(2) was directly proportional to the concentration of [C]2-AmDNT. The formation of highly polar products was also observed with [C]2-AmDNT and [U-C]PCP; these products were probably low-molecular-weight carboxylic acids. Among the aliphatic compounds tested, glyoxalate was mineralized to the greatest extent. Eighty-six percent of the COOH-glyoxalate and 9% of the CHO-glyoxalate were converted to CO(2), indicating that decarboxylation reactions may be the final step in MnP-catalyzed mineralization. The extracellular enzymatic combustion catalyzed by MnP could represent an important pathway for the formation of carbon dioxide from recalcitrant xenobiotic compounds and may also have general significance in the overall biodegradation of resistant natural macromolecules, such as lignins and humic substances.