[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › Oxygen binding: haemoglobin versus myoglobin [Biochemistry](https://durgical.com/en/biochemistry/) · Topic # Oxygen binding: haemoglobin versus myoglobin Myoglobin stores oxygen and releases it late; haemoglobin picks it up in the lung and delivers it to tissues thanks to its S-shaped curve. Updated 2026-11-01 ## Key facts - Myoglobin: one chain and one haem; hyperbolic curve, P50 ≈ 2–3 mmHg (very high affinity). - Haemoglobin: four chains (α₂β₂) and four haems; sigmoidal curve from cooperativity, P50 ≈ 26–27 mmHg, Hill coefficient ≈ 2.8. - Right shift (lower affinity, more delivery): ↑ CO₂, ↑ H⁺ (↓ pH, Bohr effect), ↑ 2,3-BPG, ↑ temperature, exercise. - Left shift (higher affinity, less delivery): HbF, CO, methaemoglobin, alkalosis, hypothermia, stored blood (low 2,3-BPG). - Haldane effect: deoxygenated haemoglobin takes up more H⁺ and CO₂; in the lung, as it is oxygenated, it releases them. ## In detail - With O₂ bound, the iron (Fe²⁺) moves into the haem plane and pulls the proximal histidine (F8); that movement passes to the other subunits and eases the next binding (T → R). - In the lung (PO₂ ≈ 100 mmHg) haemoglobin is about 98 % saturated; in resting tissue (≈ 40 mmHg) it stays at ≈ 75 %, and in exercising muscle it falls much further. - Myoglobin stays almost saturated at 40 mmHg: it gives up its O₂ only when muscle PO₂ falls very low, as a reserve. - 2,3-BPG binds in the central cavity of deoxyhaemoglobin (between the β chains) and stabilises the T form; it rises at altitude, in anaemia and in chronic hypoxia. - HbF (α₂γ₂) binds 2,3-BPG poorly, so it has higher affinity than HbA and takes O₂ from maternal blood. - CO binds haem about 200–250 times more strongly than O₂ and also shifts the curve to the left: O₂ loading and delivery both fall. - O₂ content ≈ 1.34 × Hb (g/dL) × SaO₂ + 0.003 × PaO₂: nearly all of it travels bound to haemoglobin. ## Memory aid Right shift: “CADET, face right” (CO₂, Acid, 2,3-DPG, Exercise, Temperature). **Also called** Oxyhaemoglobin dissociation curve, Bohr effect, P50 ## Clinical notes - In CO poisoning the pulse oximeter reads normal because it cannot tell carboxyhaemoglobin from oxyhaemoglobin; co-oximetry is needed. - At altitude (for example Bogotá, at about 2,600 m) 2,3-BPG and haemoglobin rise as an adaptation to the lower PO₂. - Blood stored for a long time has little 2,3-BPG and delivers O₂ poorly during the first hours after transfusion. ## Related conditions - [Carbon monoxide poisoning](https://durgical.com/en/conditions/carbon-monoxide-poisoning/) - [Methemoglobinemia](https://durgical.com/en/conditions/methemoglobinemia/) - [Sickle cell disease](https://durgical.com/en/conditions/sickle-cell-disease/) - [Thalassemias (α and β)](https://durgical.com/en/conditions/thalassemias/) ## Related - [Hemoglobin and 2,3-BPG](https://durgical.com/en/biochemistry/enzymes/hemoglobin-and-2-3-bpg/) - [Myoglobin](https://durgical.com/en/biochemistry/enzymes/myoglobin/) - [Hemoglobin variants (HbA, HbA2, HbF, HbS, HbC)](https://durgical.com/en/biochemistry/topics/hemoglobin-variants/) - [Heme](https://durgical.com/en/biochemistry/molecules/heme/) - [Allosteric and covalent regulation of enzymes](https://durgical.com/en/biochemistry/topics/allosteric-and-covalent-regulation-of-enzymes/) - [Histidine](https://durgical.com/en/biochemistry/molecules/histidine/) ## Test yourself Think of the answer, then tap the question to see it. ## Why is the haemoglobin curve sigmoidal and the myoglobin curve hyperbolic? Haemoglobin has four sites that cooperate (binding one eases the others); myoglobin has a single site. ## Which changes shift the haemoglobin curve to the right? More CO₂, more H⁺ (acidosis), more 2,3-BPG and higher temperature: affinity falls and O₂ delivery to tissue rises. ## Why does HbF have higher O₂ affinity than HbA? Its γ chains bind 2,3-BPG poorly, and 2,3-BPG normally stabilises the low-affinity form. ## What is the Haldane effect? Deoxygenated haemoglobin carries more CO₂ and H⁺; when it is oxygenated in the lung it releases them, which helps clear CO₂. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/biochemistry/topics/oxygen-binding-haemoglobin-versus-myoglobin/) Educational information, not medical advice. For any symptom, see a health professional. Sources: [PDB-101: Molecule of the Month: Hemoglobin](https://pdb101.rcsb.org/motm/41) (RCSB Protein Data Bank (PDB-101), 2026); [PDB-101: Molecule of the Month: Myoglobin](https://pdb101.rcsb.org/motm/1) (RCSB Protein Data Bank (PDB-101), 2026); [Blood gases: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003855.htm) (MedlinePlus, US National Library of Medicine, 2026); [HBB gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/hbb/) (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). [← 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/topics/oxygen-binding-haemoglobin-versus-myoglobin/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/oxygen-binding-haemoglobin-versus-myoglobin/