With the use of site-directed mutagenesis, hemoglobin has been prepared in which
ID: 58254 • Letter: W
Question
With the use of site-directed mutagenesis, hemoglobin has been prepared in which the proximal histidine residues in both the alpha and the beta subunits have been replaced by glycine. The imidazole ring from the histidine residue can be replaced by adding free imidazole in solution. Would you expect this modified hemoglobin to show cooperativity in oxygen binding? Why or why not? With the use of site-directed mutagenesis, hemoglobin has been prepared in which the proximal histidine residues in both the alpha and the beta subunits have been replaced by glycine. The imidazole ring from the histidine residue can be replaced by adding free imidazole in solution. Would you expect this modified hemoglobin to show cooperativity in oxygen binding? Why or why not? With the use of site-directed mutagenesis, hemoglobin has been prepared in which the proximal histidine residues in both the alpha and the beta subunits have been replaced by glycine. The imidazole ring from the histidine residue can be replaced by adding free imidazole in solution. Would you expect this modified hemoglobin to show cooperativity in oxygen binding? Why or why not?Explanation / Answer
No, we cannot expect this modified hemoglobin to show cooperativity in oxygen binding. When one subunit of hemoblobin is bound with oxygen, iron ion moves up into the plane of the heme. One of the axial ligands of iron and oxygen includes the imidazole ring of the proximal histidine. As the iron moves into the hemoglobin ring, it pulls the proximal histidine along with it (present in the middle of alpha helix. Thus, whenever oxygen binds to one subunit, a change in intersubunit interactions occur, this also includes alpha helix displacement. This disruption is the key for changing tensed state of hemoglobin to the relaxed state. Mutation or removal of imidazole ring from the histidine residue does not allow the cooperative binding because it is not physically connected to the -helix.
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