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Nitroxyl (NO-): a substrate for superoxide dismutase.
Stefan I Liochev1, Irwin Fridovich
1Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA.
Archives of Biochemistry and Biophysics
|June 8, 2002
Summary
Cu, Zn superoxide dismutase (SOD) interacts with nitroxyl (NO-) and nitric oxide (NO). This study reveals NO- reduces Cu, Zn SOD anaerobically and SOD catalyzes NO- elimination, independent of oxygen.
Area of Science:
- Biochemistry
- Enzymology
- Redox Biology
Background:
- Interactions between Cu, Zn superoxide dismutase (SOD) and biologically significant molecules like nitroxyl (NO-) and nitric oxide (NO) are not fully understood.
- Previous work showed NO- reduces Cu(II), Zn SOD under aerobic conditions.
Purpose of the Study:
- To investigate the anaerobic interactions of Cu, Zn SOD with NO-.
- To determine if Cu, Zn SOD can catalyze the elimination of NO- in the absence of oxygen.
- To elucidate the role of Cu, Zn SOD in NO- and NO + O2- mediated oxidation of ferrocytochrome c and NADPH.
Main Methods:
- Anaerobic and aerobic spectrophotometric assays.
- Enzyme kinetics studies.
- Measurement of cytochrome c and NADPH oxidation.
- Inhibition studies using Cu, Zn SOD.
Main Results:
- Cu, Zn SOD reduces Cu(II), Zn SOD anaerobically.
- Cu, Zn SOD catalyzes the elimination of NO- in the absence of O2.
- NO- reduces ferricytochrome c anaerobically.
- NO- and NO + O2- comparably oxidize NADPH.
- NADPH oxidation by NO + O2- is significantly more sensitive to Cu, Zn SOD inhibition than oxidation by NO-.
- Cu, Zn SOD inhibits NO- mediated NADPH oxidation via a pathway independent of O2 dismutation.
Conclusions:
- Cu, Zn SOD exhibits novel anaerobic activity with NO-.
- The enzyme plays a role in NO- metabolism beyond superoxide dismutation.
- Mechanisms for observed redox reactions and estimated rate constants are proposed.