Peroxymonocarbonate and carbonate radical displace the hydroxyl-like oxidant in the Sod1 peroxidase activity under physiological conditions
| Autor: | Ohara Augusto, Antonia T. do-Amaral, Giselle Cerchiaro, Alberto Malvezzi, Danilo B. Medinas, José Carlos de Toledo, Leandro de-Rezende |
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| Rok vydání: | 2009 |
| Předmět: |
Antioxidant
medicine.medical_treatment Bicarbonate Carbonates Toxicology Catalysis chemistry.chemical_compound medicine Organic chemistry Humans Formate Computer Simulation Nitrite Hydrogen peroxide biology Hydroxyl Radical Superoxide Dismutase General Medicine Hydrogen Peroxide Oxidants Recombinant Proteins Kinetics chemistry biology.protein Carbonate Peroxidase |
| Zdroj: | Chemical research in toxicology. 22(4) |
| ISSN: | 1520-5010 |
| Popis: | Despite being one of the most important antioxidant defenses, Cu,Zn-superoxide dismutase (Sod1) has been frequently associated with harmful effects, including neurotoxicity. This toxicity has been attributed to immature forms of Sod1 and extraneous catalytic activities. Among these, the ability of Sod1 to function as a peroxidase may be particularly relevant because it is increased in bicarbonate buffer and produces the reactive carbonate radical. Despite many studies, how this radical forms remains unknown. To address this question, we systematically studied hSod1 peroxidase activity in the presence of nitrite, formate, and bicarbonate-carbon dioxide. Kinetic analyses of hydrogen peroxide consumption and of nitrite, formate, and bicarbonate-carbon dioxide oxidation showed that the Sod1-bound hydroxyl-like oxidant functions in the presence of nitrite and formate. In the presence of bicarbonate-carbon dioxide, this oxidant is replaced by peroxymonocarbonate, which is then reduced to the carbonate radical. Peroxymonocarbonate intermediacy was evidenced by (13)C NMR experiments showing line broadening of its peak in the presence of Zn,ZnSod1. In agreement, peroxymonocarbonate was docked into the hSod1 active site, where it interacted with the conserved Arg(143). Also, a reaction between peroxymonocarbonate and Cu(I)Sod1 was demonstrated by stopped-flow experiments. Kinetic simulations indicated that peroxymonocarbonate is produced during Sod1 turnover and not in bulk solution. In the presence of bicarbonate-carbon dioxide, sustained hSod1-mediated oxidations occurred with low steady-state concentrations of hydrogen peroxide (4-10 microM). Thus, carbonate radical formation through peroxymonocarbonate may be a key event in Sod1-induced toxicity. |
| Databáze: | OpenAIRE |
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