When the oxygen-saturation curve of hemoglobin is analyzed by use of the Hill equation, a Hill constant of about 3 is found. This means that A) only 3 of the 4 hemes can bind O2. B) negative cooperativity causes hemoglobin to behave as if it had only 3 hemes that can bind O2. C) each of the 4 hemes can bond O2, but not as tightly as they would in the absence of cooperativity. D) the binding of O₂ is highly, but not perfectly, cooperative. E) 3 of the heme groups bind O₂ equally tightly, and the 4th heme binds O₂ more tightly.

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Quizplus · Accepted Answer

The Hill constant of about 3 indicates that hemoglobin exhibits high, but not perfect, cooperativity in its oxygen binding, meaning that the binding of one oxygen molecule increases the affinity of the remaining sites for oxygen, but not to the maximum theoretical level of cooperativity (which would be a Hill constant equal to the number of binding sites, i.e., 4 for hemoglobin).

When the Oxygen-Saturation Curve of Hemoglobin Is Analyzed by Use