The Bohr Effect is the decrease in oxygen affinity of hemoglobin caused by a decrease in blood pH (increase in H⁺) or an increase in partial pressure of CO2.
This physiological mechanism helps unload oxygen more efficiently in metabolically active tissues.
This physiological mechanism helps unload oxygen more efficiently in metabolically active tissues.
Why Myoglobin Does NOT Show the Bohr Effect
Myoglobin lacks the structural and functional properties required for allosteric regulation and the Bohr effect:
- It is a monomeric protein (single polypeptide chain + one heme group)
- It has no quaternary structure — no subunit interactions
- It shows no cooperative binding of oxygen (hyperbolic dissociation curve)
- It lacks the allosteric sites and conformational changes (T ↔ R state transition) needed for proton/CO2 modulation
Hemoglobin exhibits the Bohr effect because of its tetrameric structure and cooperative oxygen binding.
Myoglobin, being monomeric, binds oxygen independently with high affinity and is insensitive to pH and CO2 changes under physiological conditions.
Myoglobin, being monomeric, binds oxygen independently with high affinity and is insensitive to pH and CO2 changes under physiological conditions.
Comparison: Hemoglobin vs Myoglobin
| Property | Hemoglobin | Myoglobin |
|---|---|---|
| Structure | Tetramer (α2β2) | Monomer |
| Heme groups | 4 | 1 |
| Oxygen dissociation curve | Sigmoidal (cooperative) | Hyperbolic (non-cooperative) |
| P50 (oxygen affinity) | ≈ 26–27 mmHg | ≈ 2–3 mmHg (much higher affinity) |
| Bohr effect | Yes (strong) | No (negligible / absent physiologically) |
| Primary function | Oxygen transport in blood | Oxygen storage in muscle |
| Physiological role of pH/CO2 | Promotes O2 release in tissues | No significant effect |
Physiological Significance
Myoglobin functions as an oxygen reserve in skeletal and cardiac muscle. Its very high oxygen affinity allows it to:
- Bind O2 tightly even at moderate tissue pO2
- Release O2 only when tissue oxygen tension becomes extremely low
Because myoglobin does not respond to pH or CO2, its oxygen release is primarily controlled by local oxygen demand (pO2), not by metabolic byproducts like H⁺ or CO2 — unlike hemoglobin.