Question

With the use of site-directed mutagenesis, hemoglobin has been prepared in which the proximal histidine residues in both alpha and the beta subunits have been replaced by glycine.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. a) Would you expect this modified Hb with free imidazole to exhibit oxygen binding? Why or why not? b)Would you expect this modified hemoglobin to show cooperativity in oxygen binding? Why or why not?

Answer 1

a) No, because the heme group that has the ability to bind oxygen is bound via the imidazole ring of a histidine residue

b) The imidazole in solution bind to the heme group and then facilitates its binding to oxygen; however, protein does not have the proximal histidine residues which are capable of triggering conformational changes in the folded protein structure