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Functional coupling of oxygen binding and vasoactivity in S-nitrosohemoglobin
T J McMahon1, A E Stone, J Bonaventura
1Howard Hughes Medical Institute, Department of Medicine, and the Nicholas School for the Environment, Duke University Medical Center, Durham, North Carolina 27710, USA.
The Journal of Biological Chemistry
|April 5, 2000
Summary
S-Nitrosohemoglobin (SNO-Hb) conserves nitric oxide (NO) activity through oxygen-dependent mechanisms. This prevents excessive NO release, ensuring physiological stability and vasorelaxation.
Area of Science:
- Biochemistry
- Physiology
- Molecular Biology
Background:
- S-Nitrosohemoglobin (SNO-Hb) is a vasodilator regulated by oxygen levels.
- Vasorelaxation is linked to hemoglobin deoxygenation.
- Nitric oxide (NO) bioactivity is transduced by SNO-Hb via transnitrosation, not by NO itself.
Purpose of the Study:
- To investigate how SNO-Hb conserves its NO-related activity in vivo.
- To address the challenge of large SNO-Hb concentrations potentially leading to excessive NO release.
Main Methods:
- Studied the allosteric modulation of SNO-Hb by oxygen.
- Investigated transnitrosation reactions between SNO-Hb and thiols.
- Examined O(2) affinity changes and NO group exchange mechanisms.
Main Results:
- Increased O(2) affinity of SNO-Hb restricts NO release during deoxygenation.
- NO groups can be autocaptured by hemoglobin hemes.
- An O(2)-dependent equilibrium between SNO-Hb and iron nitrosylhemoglobin conserves NO.
Conclusions:
- Hemoglobin sequesters NO liberated during deoxygenation, preventing untimely or harmful release.
- These mechanisms ensure the physiological conservation of NO bioactivity.
- SNO-Hb's regulatory functions are crucial for maintaining vascular homeostasis.