EPR detection and characterization of lignin peroxidase porphyrin pi-cation radical.
Lignin peroxidase (LiP) from Phanerochaete chrysosporium catalyzes the H2O2 dependent one- and two-electron oxidations of substrates. The catalytic cycle involves the oxidation of ferric-LiP by H2O2 by two electrons to compound I, which is an oxoferryl heme and a free radical. It has been speculated that the unpaired electron is in a pi delocalized porphyrin radical. However, no direct evidence for the presence of the free radical has been reported. We present electron paramagnetic resonance (EPR) detection and characterization of compound I of LiP. The LiP compound I EPR signal is different than those reported previously for compound I of horseradish peroxidase and chloroperoxidase. However, the EPR signal of compound I of LiP (axial g tensor extending from gperpendicular = 3.42 to gparallel approximately 2) is very similar to the EPR signals of compound I of ascorbate peroxidase and catalase from Micrococcus lysodeikticus, in which the radical has been identified as a porphyrin pi-cation radical. On the basis of the analysis of our data and comparison with the earlier published results for compounds I of other peroxidases, we interpret the LiP compound I signal by a model for exchange coupling between an S = 1 oxyferryl [Fe = O]2+ moiety and a porphyrin pi-cation radical (S = 1/2) [Schulz, C.E., et al. (1979) FEBS Lett. 103, 102-105]. The exchange coupling is characterized by ferromagnetic rather than an antiferromagnetic interaction between the two species. The ferric-Lip EPR signal suggests that the iron in the heme is in near perfect orthogonal symmetry and provides additional evidence of the ferromagnetic interaction between the oxoferryl iron center and the porphyrin pi-cation radical.
Khindaria
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Biotechnology Center, Utah State University, Logan 84322-4705, USA.
Aust
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D001487:Basidiomycota / Q000201:enzymology; D002412:Cations; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000737:chemistry; D005609:Free Radicals; D006418:Heme / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000378:metabolism; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry; D013696:Temperature
D002412:Cations; D005290:Ferric Compounds; D005609:Free Radicals; D011166:Porphyrins; D006418:Heme; D006861:Hydrogen Peroxide; D010544:Peroxidases; C042858:lignin peroxidase