The Hill coefficient quantifies cooperativity of oxygen binding. Which statement about the Hill coefficient of hemoglobin and myoglobin is correct?

• A Hemoglobin has a Hill coefficient of 1.0, while myoglobin has a Hill coefficient of 2.8-3.0
• B Hemoglobin has a Hill coefficient of 2.8-3.0, while myoglobin has a Hill coefficient of 1.0 ✓
• C Both hemoglobin and myoglobin have Hill coefficients of 2.8-3.0
• D The Hill coefficient of hemoglobin is 4.0, reflecting its four heme groups

Explanation

Hemoglobin shows positive cooperativity with a Hill coefficient of approximately 2.8-3.0 (less than the theoretical maximum of 4 due to imperfect cooperativity). Myoglobin, being monomeric, shows no cooperativity and has a Hill coefficient of 1.0. The Hill coefficient directly reflects the degree of cooperative binding and explains the sigmoidal versus hyperbolic oxygen dissociation curves.

Reference: Lehninger Principles of Biochemistry, 7th ed.

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