In deoxyhemoglobin, the T-state is stabilized by a network of salt bridges and hydrogen bonds. Protonation of which residue contributes directly to the alkaline Bohr effect by forming an ion pair that must be broken for the T-to-R transition?

• A Valine 6 of the beta chain pairing with glutamate 6 of the partner chain
• B Histidine 146 of the beta chain pairing with aspartate 94 of the beta chain ✓
• C Proximal histidine F8 pairing with the heme iron
• D N-terminal valine of the gamma chain pairing with 2,3-BPG

Explanation

Protonated His146 beta forms a salt bridge with Asp94 beta in the same subunit, stabilizing the T-state. On oxygenation this ion pair breaks, releasing a proton, which explains the contribution of this residue to the Bohr effect. Valine 6 is involved in HbS polymerization, not T-state stabilization. The proximal histidine coordinates iron covalently rather than through a salt bridge, and 2,3-BPG binds between beta chains, not gamma chain N-termini.

Reference: Lehninger Principles of Biochemistry, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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