A manganese peroxidase (MnP) isoenzyme from Panus tigrinus CBS 577.79 was produced in a benchtop stirred-tank reactor and purified to apparent homogeneity. The purification scheme involving ultrafiltration, affinity chromatography on concanavalin–A Sepharose, and gel filtration led to a purified MnP, termed “MnP II,” with a specific activity of 288 IU mg−1 protein and a final yield of 22%. The enzyme turned out to be a monomeric protein with molecular mass of 50.5 kDa, pI of 4.07, and an extent of N-glycosylation of about 5.3% of the high-mannose type. The temperature and pH optima for the formation of malonate manganic chelates were 45 °C and 5.5, respectively. MnP II proved to be poorly thermostable at 50 and 60 °C, with half-lives of 11 min and 105 s, respectively. Km values for H2O2 and Mn2+ were 16 and 124 μM, respectively. Although MnP II was able to oxidize veratryl alcohol and to catalyze the Mn2+-independent oxidation of several phenols, it cannot be assigned to the versatile peroxidase family. As opposed to versatile peroxidase oxidation, veratryl alcohol oxidation required the simultaneous presence of H2O2 and Mn2+; in addition, low turnover numbers and Km values higher than 300 μM characterized the Mn2+-independent oxidation of substituted phenols. Kinetic properties and the substrate specificity of the enzyme markedly differed from those reported for MnP isoenzymes produced by the reference strain P. tigrinus 8/18. To our knowledge, this study reports for the first time a thorough electrochemical characterization of a MnP from this fungus.
Manganese peroxidase Purification Panus tigrinusPhenols Direct electron transfer
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This work was carried out with the financial support of “Sapienza” University of Rome and of the European Commission under contract number 017350 (BioMedNano).