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Homolytic pathways drive peroxynitrite-dependent Trolox C oxidation.
Horacio Botti1, Madia Trujillo, Carlos Batthyány
1Departamento de Bioquímica and Center for Free Radical and Biomedical Research, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay.
Chemical Research in Toxicology
|October 19, 2004
Summary
Peroxynitrite, a potent oxidant, indirectly oxidizes Trolox C (an alpha-tocopherol analog) via carbon dioxide or proton catalysis. This reaction mechanism is crucial for understanding alpha-tocopherol
Area of Science:
- Biochemistry
- Oxidative Stress Research
- Antioxidant Mechanisms
Background:
- Peroxynitrite is a key mediator in nitric oxide and superoxide-dependent toxicity.
- Alpha-tocopherol is a critical lipid-soluble antioxidant, and its reactions with peroxynitrite are biologically relevant.
- Previous studies suggested a direct reaction between peroxynitrite and Trolox C (TxOH), a water-soluble alpha-tocopherol analog, which prompted further investigation.
Purpose of the Study:
- To elucidate the kinetics and mechanism of the reaction between peroxynitrite and Trolox C (TxOH).
- To investigate the modulatory effect of carbon dioxide (CO2) on this reaction.
- To clarify the role of peroxynitrite-derived radicals in Trolox C oxidation.
Main Methods:
- Electron paramagnetic resonance (EPR) spectroscopy to detect radical species.
- Stopped-flow spectrophotometry to study reaction kinetics.
- Investigated reactions in the presence and absence of CO2.
Main Results:
- The reaction between peroxynitrite and TxOH is indirect, with Trolox C phenoxyl radical (TxO*) and Trolox C quinone (TxQ) as key products.
- The reaction rate is dependent on peroxynitrite and CO2 concentration, indicating a catalytic role for CO2.
- TxOH did not inhibit direct peroxynitrite-mediated oxidation of methionine, supporting an indirect mechanism.
Conclusions:
- Protonation or CO2-catalyzed homolysis of peroxynitrite is essential for the oxidation of TxOH and, by extension, alpha-tocopherol.
- The findings clarify the indirect mechanism of peroxynitrite-induced oxidation of Trolox C, highlighting the importance of reaction conditions.