A significant contribution to the change in hemoglobin affinity for oxygen from pH 7.2 to pH 7.6 is due to a change in the protonation state of which amino acid side chain?
A) Cys
B) His
C) Ser
D) Asp
E) Lys

Question

Quizplus · Accepted Answer

The amino acid side chain that gets protonated and deprotonated between pH 7.2 and pH 7.6 is histidine (His). When pH increases from 7.2 to 7.6, the imidazole ring on histidine gets deprotonated, resulting in a negative charge on the nitrogen atom. This negative charge repels the negatively charged oxygen atoms in the heme group, causing the hemoglobin to release oxygen more readily.

A Significant Contribution to the Change in Hemoglobin Affinity for Oxygen