Written by Merel Dagher
Which of the following increases the affinity for binding oxygen in hemoglobin?
a. H+ ions increasing
b. CO2 concentration increasing
c. 2,3-BPG concentration increasing
d. Stabilization of the T-state
e. exchanging a His for Ser residue in Hb
a. H+ ions increasing
b. CO2 concentration increasing
c. 2,3-BPG concentration increasing
d. Stabilization of the T-state
e. exchanging a His for Ser residue in Hb
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The correct answer is e. Hb has a low affinity for oxygen (relative to myoglobin or HbF), especially in the T state. a, b, and c all describe conditions that would result in the shift of Hb from its R-state (which has a higher affinity for binding oxygen) to its T-state (which has a lower affinity for binding oxygen and will release it). Exchanging a His residue for a Ser residue is actually what takes place in fetal Hb, and that increases the affinity for oxygen because it doesn’t bind attract 2,3-BPG as much as Hb does. Remember that 2,3-BPG is highly negatively charged and histidine is one of the positively charged polar amino acids. Serine, on the other hand, is polar but not charged.