[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › Nitric oxide (NO)

[Biochemistry](https://durgical.com/en/biochemistry/) · Molecule

# Nitric oxide (NO)

Nitric oxide is a short-lived gas made in the body that widens blood vessels, acts as a nerve messenger and is used by immune cells to kill microbes.

Updated 2026-11-01

Loading the 3D model…

## Key facts

- A free radical gas that diffuses across membranes; its half-life in blood is only seconds.
- Its main receptor is soluble guanylyl cyclase (binds its haem): cGMP rises and smooth muscle relaxes.
- It was identified as the endothelium-derived relaxing factor; it also inhibits platelet aggregation and leukocyte adhesion.
- Haemoglobin inactivates it quickly (forming nitrate and methaemoglobin); with superoxide it forms toxic peroxynitrite.

**Also called**
Endothelium-derived relaxing factor (EDRF)

**Formula**
NO

**PubChem**
[CID 145068](https://pubchem.ncbi.nlm.nih.gov/compound/145068)

## Structure

- One nitrogen and one oxygen with an unpaired electron (a radical).

## Clinical notes

- Inhaled NO dilates pulmonary vessels in persistent pulmonary hypertension of the newborn.
- Nitroglycerin and nitroprusside act by releasing NO; nitroprusside can also release cyanide.
- Macrophages use NO from iNOS against bacteria and parasites; excess NO drives the vasodilation of septic shock.

## Related conditions

- [Arterial hypertension](https://durgical.com/en/conditions/arterial-hypertension/)
- [Stable angina](https://durgical.com/en/conditions/stable-angina/)
- [Erectile dysfunction](https://durgical.com/en/conditions/erectile-dysfunction/)
- [Sepsis and septic shock](https://durgical.com/en/conditions/sepsis-and-septic-shock/)
- [Methemoglobinemia](https://durgical.com/en/conditions/methemoglobinemia/)

## Related

- [Nitric oxide synthase (NOS)](https://durgical.com/en/biochemistry/enzymes/nitric-oxide-synthase/)
- [Hemoglobin and 2,3-BPG](https://durgical.com/en/biochemistry/enzymes/hemoglobin-and-2-3-bpg/)
- [Reactive oxygen species and antioxidants](https://durgical.com/en/biochemistry/topics/reactive-oxygen-species-and-antioxidants/)
- [Superoxide dismutase (SOD)](https://durgical.com/en/biochemistry/enzymes/superoxide-dismutase/)

## Test yourself

Think of the answer, then tap the question to see it.

## What enzyme is the main receptor of nitric oxide?

Soluble guanylyl cyclase, whose haem binds NO and raises cGMP.

## Why does nitric oxide act only locally?

It is a reactive radical inactivated within seconds, especially by haemoglobin.

## What toxic compound forms when NO meets superoxide?

Peroxynitrite (ONOO⁻), which damages proteins, lipids and DNA.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/biochemistry/molecules/nitric-oxide/)

Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Nitric Oxide (CID 145068)](https://pubchem.ncbi.nlm.nih.gov/compound/145068) (PubChem, NCBI, 2026); [PDB-101: Molecule of the Month: Nitric Oxide Synthase](https://pdb101.rcsb.org/motm/133) (RCSB Protein Data Bank (PDB-101), 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

[← All of biochemistry](https://durgical.com/en/biochemistry/)

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/biochemistry/molecules/nitric-oxide/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/molecules/nitric-oxide/