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
Loading the 3D model…
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
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
Related
- Hemoglobin and 2,3-BPG
- Heme
- Hemoglobin variants (HbA, HbA2, HbF, HbS, HbC)
- 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.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: MB: Myoglobin (human) (UniProt, 2026); 3RGK: Crystal Structure of Human Myoglobin Mutant K45R (RCSB Protein Data Bank, 2026); Myoglobin blood test: MedlinePlus Medical Encyclopedia (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).
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.