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Lignin peroxidases can also oxidize manganese
A Khindaria1, D P Barr, S D Aust
1Biotechnology Center, Utah State University, Logan 84322-4705, USA.
Biochemistry
|June 13, 1995
Summary
Lignin peroxidases from Phanerochaete chrysosporium directly oxidize manganese (Mn2+) to manganese (Mn3+), challenging previous free radical mediation theories. This study characterizes this novel manganese peroxidase activity in lignin peroxidases.
Area of Science:
- Biochemistry
- Enzymology
- Fungal Metabolism
Background:
- White rot fungus *Phanerochaete chrysosporium* secretes lignin peroxidases (LiPs) and manganese-dependent peroxidases (MnPs).
- LiPs are major isozymes traditionally believed to directly oxidize substrates.
- MnPs are minor isozymes involved in manganese oxidation.
Purpose of the Study:
- To investigate the manganese peroxidase activity of lignin peroxidases.
- To characterize the reaction kinetics of LiP isozyme H2 (LiPH2) with manganese.
- To determine the mechanism of Mn2+ oxidation by LiPs.
Main Methods:
- Transient state and steady-state kinetic studies using LiPH2.
- Monitoring the formation of Mn3+-oxalate.
- Electron spin resonance (ESR) and oxygen evolution studies.
Main Results:
- LiPH2 catalyzes the H2O2-dependent oxidation of Mn2+ to Mn3+.
- Second-order rate constant for LiPH2-compound I with Mn2+ is 4.2 x 10(4) M-1 S-1 at pH 6.0.
- Mn2+-oxalate binds and reduces LiPH2-compound II to ferric enzyme with a first-order rate constant of 215 +/- 6 S-1.
Conclusions:
- Lignin peroxidases possess manganese peroxidase activity.
- The oxidation of Mn2+ by LiPs is a direct enzymatic process, not mediated by free radicals.
- This finding expands the known catalytic repertoire of lignin peroxidases.