Why does the initial oxygen binding event cause the oxygen binding curve to hemo

Question

Why does the initial oxygen binding event cause the oxygen binding curve to hemoglobin to be sigmoidal?

            A) The initial oxygen directly pulls all hemes into a binding-competent state

            B) The initial oxygen binding at one site locks in a conformational change to make all other sites binding competent

            C) The initial oxygen binds at a secondary site which changes the conformation of hemoglobin from L to T

            D) Oxygen binds to a histadine (H143) and prevents it from being protonated, which locks hemoglobin in a binding-competent state

            E) Oxygen increases the blood pH, and through the Bohr effect more oxygens can then bind to hemoglobin

Explanation / Answer

Ans : B) The initial oxygen binding at one site locks in a conformational change to make all other sites bonding competent.

The co-operative binding of the oxygen takes place with the 4-polypeptide chains. When one subunit has already bounded with oxygen , the ability of hemoglobin to bind with the other oxygen atoms increases. This gives a characteristic sigmoid shape to the curve.

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