The Hill coefficient (n) derived from the Hill plot describes the degree of cooperativity of ligand binding. For normal adult hemoglobin, the Hill coefficient at half-saturation is approximately:
- A 0.5
- B 1.0
- C 2.8 ✓
- D 4.0
Correct answer: C. 2.8
Explanation
Normal hemoglobin has a Hill coefficient of about 2.8, indicating strong positive cooperativity among its four subunits. A value of 1.0 would indicate no cooperativity, as seen in myoglobin, while 4.0 would represent perfect all-or-none switching between fully deoxy and fully oxy states, which real hemoglobin does not achieve because intermediate ligation states exist. Values below 1 indicate negative cooperativity, which does not apply here.
Reference: Lippincott Illustrated Reviews: Biochemistry, 7th ed.
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