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Veratryl alcohol oxidation by lignin peroxidase
A Khindaria1, I Yamazaki, S D Aust
1Department of Chemistry and Biochemistry, Utah State University, Logan 84322, USA.
Biochemistry
|December 26, 1995
Summary
Lignin peroxidase (LiP) from Phanerochaete chrysosporium oxidizes veratryl alcohol (VA) to veratryl aldehyde (VAD). Oxalate inhibits LiP by interacting with a veratryl alcohol cation radical (VA.+) intermediate bound to LiP compound II (LiPII).
Area of Science:
- Biochemistry
- Enzymology
- Fungal metabolism
Background:
- Lignin peroxidase (LiP) from Phanerochaete chrysosporium is a key enzyme in lignin degradation.
- LiP catalyzes the oxidation of veratryl alcohol (VA) to veratryl aldehyde (VAD) via a H2O2-dependent mechanism.
- The precise mechanism of VA oxidation by LiP, particularly the role of LiP intermediates, requires further elucidation.
Purpose of the Study:
- To investigate the detailed mechanism of veratryl alcohol (VA) oxidation by lignin peroxidase (LiP).
- To elucidate the role of LiP intermediates, including LiP compound I (LiPI) and LiP compound II (LiPII), in VA oxidation.
- To determine the effect of oxalate on LiP activity and the underlying mechanistic basis.
Main Methods:
- Enzyme kinetics studies involving LiP, H2O2, and VA at pH 4.5.
- Investigation of the effect of oxalate on LiP turnover rate and rate constants.
- Electron spin resonance (ESR) spectroscopy to detect and quantify veratryl alcohol cation radical (VA.+) intermediates.
- Spectroscopic analysis of LiPII during VA oxidation.
Main Results:
- The rate constant for LiPII reduction by VA was insufficient to explain the observed LiP turnover rate.
- Oxalate decreased LiP turnover but did not affect rate constants for LiP, LiPI, or LiPII with H2O2 or ferrocyanide-reduced LiPI.
- An oxalate-sensitive burst phase in LiPII reduction by VA suggested two states of VA.+ bound to LiPII, one ESR-active and one ESR-silent.
- ESR measurements confirmed the presence of both ESR-active and ESR-silent VA.+ species, both of which were eliminated by oxalate.
Conclusions:
- Oxalate inhibits LiP by reacting with the veratryl alcohol cation radical (VA.+) bound to LiP compound II (LiPII).
- A proposed mechanism involves a complex of LiPII and VA.+ reacting with another VA molecule to form veratryl aldehyde (VAD).
- The presence of both ESR-active and ESR-silent VA.+ species bound to LiPII is crucial for understanding the reaction pathway.