Oxygen dissociation curve
Tip
When oxygen supply is insufficient, the body initially reduces the affinity of red blood cells for oxygen, ensuring adequate oxygen supply to peripheral tissues.
- Causes of shift to the right include:
- ↑ Partial pressure of carbon dioxide (↑ PCO2)
- ↑ Body temperature (e.g., fever)
- ↑ H+ (↓ pH)
- ↑ 2,3-BPG (generated by 2,3-BPG mutase during erythrocyte glycolysis)
- 2,3-bisphosphoglycerate (2,3-BPG) concentrations increase in erythrocytes when oxygen availability is reduced, as occurs in chronic lung disease, heart failure, and chronic exposure to high altitudes.
- 2,3-BPG is synthesized from glycolytic intermediates and binds strongly to deoxyhemoglobin in a pocket formed between the 2 beta chains. This binding reduces the oxygen affinity of hemoglobin, allowing more oxygen to diffuse into the peripheral tissues. The hemoglobin 2,3-BPG binding pocket contains positively charged amino acids (eg, histidine and lysine) that attract the negatively charged phosphate groups in 2,3-BPG. Mutations that decrease the positive charge of the binding site decrease 2,3-BPG binding and increase hemoglobin oxygen affinity.
- During normal glycolysis, ATP is generated when 1,3-BPG is converted to 3-phosphoglycerate by the enzyme phosphoglycerate kinase. However, erythrocytes can bypass this part of the pathway using bisphosphoglycerate mutase, an enzyme that converts 1,3-BPG to 2,3-BPG in a step that produces no ATP.
- During normal glycolysis, ATP is generated when 1,3-BPG is converted to 3-phosphoglycerate by the enzyme phosphoglycerate kinase. However, erythrocytes can bypass this part of the pathway using bisphosphoglycerate mutase, an enzyme that converts 1,3-BPG to 2,3-BPG in a step that produces no ATP.
- ↑ Exercise
- ↑ Altitude
- Causes of shift to the left include:
- ↓ Partial pressure of carbon dioxide (PCO2)
- ↓ Body temperature
- ↓ H+ (↑ pH)
- ↓ 2,3-BPG (e.g., due to mutations in the BPGM gene on chromosome 7)
- ↑ CO
- ↑ Methemoglobin
- ↑ Fetal hemoglobin (HbF)