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

# Myoglobin

Myoglobin stores oxygen inside muscle; it has a single heme and gives it up only when oxygen falls very low.

Updated 2026-11-01

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## Key facts

- A single chain of 153 amino acids with eight helices (A–H) and one heme; it binds one O₂ molecule.
- Hyperbolic saturation curve (no cooperativity); P50 about 2–3 mmHg versus about 26 mmHg for hemoglobin.
- It is not affected by 2,3-BPG, CO₂ or pH (no Bohr effect).
- The proximal histidine (F8) binds the iron; the distal one (E7) stabilises O₂ and lowers CO affinity.

**Genes**
MB

**Structure (PDB)**
[3RGK](https://www.rcsb.org/structure/3RGK)

## Structure

- Structure 3RGK is human myoglobin (K45R variant, a surface change far from the heme) with its heme group.
- It was the first protein whose 3D structure was solved by X-ray (Kendrew, 1958, sperm whale myoglobin).

## Regulation

- It is abundant in type I (red, oxidative) muscle fibres and in the heart; it rises with endurance training and altitude.

## Inhibitors and toxins

- Carbon monoxide (binds the heme iron)
- Oxidants that turn Fe²⁺ into Fe³⁺ (metmyoglobin)

## Clinical notes

- Rhabdomyolysis: released myoglobin is filtered and damages the renal tubule (acute kidney injury); urine is dark and the dipstick is positive for blood without red cells.
- It rises in blood 1–3 hours after muscle or heart injury; it is sensitive but not specific, which is why troponin replaced it for myocardial infarction.
- Causes of rhabdomyolysis: crush injury, compartment syndrome, extreme exercise, seizures, statins, heat stroke.

## Related conditions

- [Acute kidney injury](https://durgical.com/en/conditions/acute-kidney-injury/)
- [Acute compartment syndrome](https://durgical.com/en/conditions/acute-compartment-syndrome/)
- [Myocardial Infarction (Heart Attack)](https://durgical.com/en/conditions/myocardial-infarction/)

## Related

- [Hemoglobin and 2,3-BPG](https://durgical.com/en/biochemistry/enzymes/hemoglobin-and-2-3-bpg/)
- [Heme](https://durgical.com/en/biochemistry/molecules/heme/)
- [Hemoglobin variants (HbA, HbA2, HbF, HbS, HbC)](https://durgical.com/en/biochemistry/topics/hemoglobin-variants/)
- [Heme breakdown and bilirubin](https://durgical.com/en/biochemistry/pathways/heme-breakdown-and-bilirubin/)

## Test yourself

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

## Why is the myoglobin curve hyperbolic and the hemoglobin curve sigmoid?

Myoglobin has a single binding site; hemoglobin has four that cooperate.

## How does myoglobin harm the kidney in rhabdomyolysis?

It is filtered by the glomerulus, blocks the tubules, and its heme causes oxidative damage: acute kidney injury.

## Which urine finding suggests myoglobinuria?

A dipstick positive for blood with no red cells under the microscope.

## Does myoglobin respond to 2,3-BPG?

No: it is a monomer with no central cavity; 2,3-BPG acts only on hemoglobin.

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

Sources: [MB: Myoglobin (human)](https://www.uniprot.org/uniprotkb/P02144/entry) (UniProt, 2026); [3RGK: Crystal Structure of Human Myoglobin Mutant K45R](https://www.rcsb.org/structure/3RGK) (RCSB Protein Data Bank, 2026); [Myoglobin blood test: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003663.htm) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/biochemistry/enzymes/myoglobin/
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