Manganese Peroxidase (MnP)

Manganese Peroxidase, a fungal enzyme, is a hemoprotein involved in the oxidative degradation of lignin in white-rot basidiomycetes. It catalyzes the oxidation of Mn(II) to Mn(III) by H2O2. The highly reactive Mn(III) is stabilized via chelation in the presence of dicarboxylic acid: \n2 Mn(II) + 2 H+ + H2O2 ? 2 Mn(III) + 2 H2O \n\nThe 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-14C]pentachlorophenol ([U-14C]PCP), [U-14C]catechol, [U-14C]tyrosine, [U-14C]tryptophan, [4,5,9,10-14C]pyrene, and [ring U-14C]2-amino-4,6-dinitrotoluene ([14C]2-AmDNT), to 14CO2. Mineralization was dependent on the ratio of MnP activity to concentration of reduced glutathione (thiol-mediated oxidation), a finding which was demonstrated by using [14C]2-AmDNT as an example. At [14C]2-AmDNT concentrations ranging from 2 to 120 microM, the amount of released 14CO2 was directly proportional to the concentration of [14C]2-AmDNT. The formation of highly polar products was also observed with [14C]2-AmDNT and [U-14C]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 14COOH-glyoxalate and 9% of the 14CHO-glyoxalate were converted to 14CO2, 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.\n \nManganese peroxidase (MnP) (EC 1.11.1.13) is a heme-containing glycoprotein that requires hydrogen peroxide (H2O2) as an oxidant (7, 17). This enzyme is produced only by ligninolytic basidiomycetes (white rot fungi and litter-decaying fungi) (3, 11). MnP oxidizes Mn(II) to Mn(III), which then oxidizes phenolic rings to phenoxy radicals, leading finally to the decomposition of compounds (8, 32). Due to its high reactivity, Mn(III) has to be stabilized via chelation by dicarboxylic acids, such as malonate or lactate (37). In addition to phenolic structures, the MnP system has been reported to catalyze cleavage of nonphenolic lignin model compounds (5, 9, 14, 20). Evidence that MnP plays a crucial role in biodegradation of macromolecular substances is accumulating; e.g., this enzyme plays a role in the depolymerization of lignin (14, 36), in the bleaching of pulp (10, 27), and in the decomposition of humic substances (13).\n\nDue to the nonspecificity of Mn(III), the MnP system is also able to oxidize a variety of organic pollutants and xenobiotic compounds. Thus, the conversion of 4-amino-2-nitrotoluene (33), polycyclic aromatic hydrocarbons, including creosote (2, 4, 26), and chlorolignin-containing wastes (18) has been described previously. We have recently described partial mineralization of [ring U-14C]2-amino-4,6-dinitrotoluene ([14C]2-AmDNT), a main metabolite of the explosive 2,4,6-trinitrotoluene, by a crude preparation of MnP from the South American white rot fungus Nematoloma frowardii (29). The present paper describes the enzymatic combustion of a broad spectrum of aromatic and aliphatic substances by the MnP system of N. frowardii and demonstrates the universal validity of the degradation principle. Furthermore, dependence of the mineralization process on the concentration of the peptide glutathione (GSH) is demonstrated. The concept of enzymatic combustion was adopted from wood microbiology; this concept has been used to describe the depolymerization of high-molecular-weight lignin by nonspecific extracellular peroxidases from ligninolytic fungi (15).\n\nUnit Definition:\nOne unit is defined as the amount of enzyme that oxidizes 1umole of Mn(II) per minute at pH 4.5 and 25 degrees C.\n\nReaction Conditions:\nOptimal reaction at pH 4.5, 25 degrees C with a wavelength of 270nm and a light path of 1cm.\n\nStorage and Stability:\nLyophilized powder may be stored at -20 degrees C. Stable for 12 months at -20 degrees C. Reconstitute with ddH2O. Aliquot to avoid repeated freezing and thawing. Store at -20 degrees C. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap. Further dilutions can be made in assay buffer.

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SPECIFICATIONS

Catalog Number

M2195

Size

200U

Form

Supplied as a brown lyophilized powder

References

1. Hofrichter, M., et al., Appl. Environ. Microbiol. 64: 399-404 (1998). 2. Wariishi, H., et al., J. Biol. Chem. 2676: 23,688-23,695 (1992). 3. Appl. Environ. Microbiol. 64(2): 399

Alternative Names

EC=1.11.1.13