The Bohr effect describes the decreased oxygen affinity of hemoglobin in acidic, high-CO2 environments (tissues). The molecular mechanism involves protonation of which key residue that stabilizes the T (tense/deoxy) conformation?
- A Histidine beta-146 (His HC3 of the beta chain), which forms a salt bridge with Asp beta-94 when protonated ✓
- B Lysine alpha-141, which interacts with the alpha1-beta2 interface
- C Arginine beta-143, which directly binds heme iron
- D Glutamate beta-6, which stabilizes the quaternary structure
Correct answer: A. Histidine beta-146 (His HC3 of the beta chain), which forms a salt bridge with Asp beta-94 when protonated
Explanation
The Bohr effect's key molecular basis is the protonation of His HC3 (His-beta-146) in acidic conditions. When protonated, this histidine forms an intrachain salt bridge with Asp-beta-94, stabilizing the T (deoxy) conformation and releasing oxygen. At the lungs (alkaline, low CO2), His-beta-146 loses a proton, the salt bridge breaks, and hemoglobin shifts to the R (oxy) conformation with high O2 affinity. This proton release by hemoglobin in the lungs is exploited by the bicarbonate/CO2 system. Glu-beta-6 is mutated in sickle cell anemia but does not mediate the Bohr effect.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.