The Bohr effect describes rightward shift of the oxygen-haemoglobin dissociation curve at low pH/high CO2, facilitating O2 delivery to tissues. At the molecular level, this occurs because:

• A CO2 competes with O2 for the haem iron binding site
• B Protons (H+) bind specific histidine residues (His146 beta-chain) stabilising the T (deoxy) conformation and reducing O2 affinity ✓
• C Carbamino-Hb formation at alpha-amino groups directly displaces O2 from haem
• D CO2 increases 2,3-DPG binding to the central cavity, reducing O2 affinity

Explanation

H+ ions preferentially bind His146 of the beta-chains (and the N-terminal alpha-amino group of the alpha-chain) in the T state, stabilising salt bridges that maintain the low-affinity T-state conformation; this reduces O2 affinity, releasing O2 in metabolically active (acidic) tissues. Carbamino-CO2 also stabilises the T state but acts on different sites. 2,3-DPG binds the central cavity but is not the Bohr mechanism. CO2 does not compete at haem iron.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.