The Bohr effect describes decreased oxygen affinity of hemoglobin at lower pH and higher CO2. At the tissue level (low pH, high pCO2), hemoglobin releases oxygen more readily. At the molecular level, CO2 contributes to this effect by:

• A Directly oxidizing Fe2+ in heme to Fe3+, reducing oxygen binding
• B Forming carbamino compounds by reacting with N-terminal alpha-amino groups of globin chains, stabilizing the deoxy (T) conformation ✓
• C Competing with oxygen for the same binding site on the heme iron
• D Activating phosphofructokinase in erythrocytes to increase 2,3-BPG

Explanation

CO2 reacts non-enzymatically with the free alpha-amino groups of the N-terminal valine residues of both alpha and beta chains to form carbamino-hemoglobin (carbaminohemoglobin); this reaction adds a negative charge (carbamate) to the terminal amino group. These carbamate groups form additional salt bridges that stabilize the T (tense, deoxy) conformation of hemoglobin, lowering oxygen affinity and facilitating O2 unloading at tissues. Simultaneously, CO2 is hydrated to H2CO3/HCO3-/H+ by carbonic anhydrase in erythrocytes; the resulting decrease in pH protonates histidine 146 on the beta chain, further stabilizing the T state (classic Bohr effect).

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.