The binding of O_2 to hemoglobin exhibits \'cooperative\' effect. Briefly explai

Question

The binding of O_2 to hemoglobin exhibits 'cooperative' effect. Briefly explain the phenomenon of cooperatively exhibited by the hemoglobin molecules in the binding of oxygen. The reversible hydration of carbon dioxide (CO_2/HCO_3) is catalyzed with a remarkable rate enhancement by a metallic-protein called carbonic anhydrase (CA). a. Write the equation for the hydration of CO_2. b. What is the active metal center in CA? c. Briefly describe the coordination mode of the metal ion in CA to histidine in its active or resting state.

Explanation / Answer

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One of the unique features of hemoglobin is that it exhibits co-operativity. This means that hemoglobin can transmit intra-molecular messages to its various functional groups to help it attain a maximum affinity for the ligand of interest. The affinity of hemoglobin is proportional to the quantity of oxygen bound at a given time.

There are two main models of cooperativity for hemoglobin. Hb has 2 conformations: T (tense) form deoxy-Hb low O2 affinity and R (relaxed) form oxy-Hb high O2 affinity

O2 binding generates conversion between 2 conformations. When O2 is bound it is in the O2- form O2 binds to iron in heme group When no O2 is bound, Fe sticks out of the plane, when O2 is bound, Fe is w/in the plane. His is responsible for this conformation change in cooperativity. The hemoglobin molecule changes rapidly between its R- and T-states in order to maximize its affinity for oxygen. Hemoglobin is constantly "flipping" back and forth between states in an attempt to bind as much oxygen as possible.One strand of hemoglobin starts a sequence of conformational changes in hemoglobin that increase its affinity for oxygen. When one strand of hemoglobin binds oxygen, the hemoglobin rearranges in a manner that favors additional oxygen binding. When the next oxygen is bound, another conformational change occurs to further supplement binding; thus, hemoglobin can sequentially increase its affinity for oxygen as more and more of its strands bind oxygen.

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