Why sickle hemoglobin polymerizes when deoxygenated
In sickle cell disease, a glutamate-to-valine substitution makes hemoglobin S polymerize. Why does polymerization happen mainly when HbS is deoxygenated?
Answer B: explanation for every choice
A
Valine has no sulfur and can't form disulfide bonds.
B
Correct. The surface valine fits a hydrophobic site that is accessible only in the deoxy conformation, so low oxygen promotes fiber formation.
C
This reverses the relationship. Oxygenation reduces polymerization.
D
Fe³⁺ hemoglobin (methemoglobin) is a separate condition. The mutation is in the globin chain, not the heme.
TakeawayHbS polymerizes in the deoxy state. Low O2, dehydration, and acidosis promote sickling.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb155.