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Updated: Jul 20, 2026
11:28
Analytical Techniques for Assaying Nitric Oxide Bioactivity
Published on: June 18, 2012
[Nitric oxide and hemoglobin]
1Department of Biochemistry & Biophysics, University of Pennsylvania Medical Center, Philadelphia 19104-6089, USA.
Nihon Yakurigaku Zasshi. Folia Pharmacologica Japonica
|October 30, 1998
Summary
Nitric oxide (NO) is produced by endothelial cells and regulates vascular tone. Hemoglobin (Hb) scavenges excess NO, facilitating oxygen delivery and maintaining blood homeostasis.
Area of Science:
- Biochemistry
- Physiology
- Molecular Biology
Context:
- Nitric oxide (NO) is synthesized by nitric oxide synthases (NOS) in endothelial cells.
- NO acts as a paracrine signaling molecule, activating soluble guanylyl cyclase (sGC) and producing cyclic guanosine monophosphate (cGMP).
- Maintaining steady-state plasma concentrations of NO is crucial for vascular tone and circulation.
Purpose:
- To elucidate the intricate balance between NO production and scavenging by hemoglobin (Hb) in erythrocytes.
- To explain the molecular mechanism by which Hb sequesters NO and its impact on Hb conformation and oxygen affinity.
- To describe the NO-Hb-O2 interaction and its role in maintaining blood homeostasis and oxygen delivery.
Summary:
- Under physiological conditions, deoxy hemoglobin (Hb) tightly binds NO to its alpha-subunits, forming alpha-nitrosyl Hb.
- NO binding induces a conformational shift in Hb to a T-state, enhancing oxygen (O2) carrying capacity of beta-subunits.
- NO sequestered in Hb is eventually oxidized to nitrate (NO3-), with methemoglobin (Met Hb) being reduced back to deoxy Hb, completing the NO scavenging cycle.
Impact:
- NO-induced conformational changes in Hb and sGC share a common molecular mechanism involving heme Fe-proximal His bond cleavage.
- Hb's ability to sequester NO ensures its function as an effective O2 carrier despite NO binding.
- This NO-Hb interaction contributes to vasodilation, increased blood flow, and potentially enhanced peripheral oxygen delivery.
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