title: Lignin peroxidases can also oxidize manganese.
abstract: The peroxidase isozymes secreted by the white rot fungus Phanerochaete chrysosporium include lignin peroxidases and manganese-dependent peroxidases. The major isozymes, called lignin peroxidases, are thought to oxidize chemicals directly. The manganese-dependent peroxidases (H3, H4, H5, and H9) are relatively minor, making up only a fraction of the total peroxidase protein. However, we have found that lignin peroxidases will also catalyze the H2O2-dependent oxidation of Mn2+ to Mn3+. We have used lignin peroxidase isozyme H2 (LiPH2) to characterize the manganese peroxidase activity of lignin peroxidases. Transient state kinetic studies were used to obtain a second-order rate constant of 4.2 x 10(4) M-1 S-1 for the reaction of LiPH2-compound I with free or chelated Mn2+ at pH 6.0. This reaction was too fast to monitor at pH 4.5. Only chelated Mn2+ could reduce LiPH2-compound II to ferric enzyme. The Mn(2+)-chelate (oxalate) first bound LiPH2-compound II with a Kd of (1.5 +/- 0.3) x 10(-5) M and then reduced LiPH2-compound II to ferric enzyme with a first order rate constant of 215 +/- 6 S-1. Steady-state kinetic studies on LiPH2 were performed by directly monitoring the formation of Mn(3+)-oxalate. These results show that oxidation of Mn2+ by a lignin peroxidase does not occur through free radical mediation as proposed previously [Popp et al. (1990) Biochemistry 29, 10475-10480). Electron spin resonance and oxygen evolution studies also indicate that Mn2+ is directly oxidized by LiPH2.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Biotechnology Center, Utah State University, Logan 84322-4705, USA.
authors.forename: A
authors.initials: A
authors.lastname: Khindaria
authors.forename: D P
authors.initials: DP
authors.lastname: Barr
authors.forename: S D
authors.initials: SD
authors.lastname: Aust
mesh_terms: D001487:Basidiomycota / Q000201:enzymology*; D001592:Benzyl Alcohols / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D008345:Manganese / Q000378:metabolism*; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000378:metabolism*
chemical_list: D001592:Benzyl Alcohols; D008345:Manganese; D010544:Peroxidases; C042858:lignin peroxidase; C042197:veratryl alcohol