The cooperative binding of $\mathrm{O}_{2}$ in hemoglobin is due to
(a)a decrease in size of iron followed by changes in the protein conformation
(b)an increase in size of iron followed by changes in the protein conformation
(c)a decrease in size of iron that is NOT accompanied by the protein conformational changes
(d)an increase in size of iron that is NOT accompanied by the protein conformational changes
Answer
Answer: A ✓ checked by 4AB · confidence high
Explanation
On binding O₂ the iron becomes low-spin and smaller, drops into the porphyrin plane and pulls the proximal histidine with it; that movement propagates through the protein (T → R) and raises the affinity of the other subunits.