Question

About two dozen histidine residues in hemoglobin are involved in binding the protons produced by cellular metabolism. in this manner, hemoglobin contributes to buffering in the blood, and the imidazole groups able to bind and release protons contribute to the bohr effect. one important contributor to the bohr effect is his 146 on the β chain of hemoglobin, whose side chain is in close proximity to the side chain of asp 94 in the deoxy form of hemoglobin but not the oxy form.
a. what kind of interaction occurs between asp 94 and his 146 in deoxyhemoglobin?
b. the proximity of asp 94 alters the pk value of the imidazole ring of his. in what way?

Answer 1

A) The answer is allosteric interaction where activators or repressors bind to a protein, other than the protein active site, hence changing the protein conformation. This interaction occurs between the heme subunits of haemoglobin.
b) Through protonation. The amino group of the alpha subunits and the histidine C-terminal of beta subunits acquire H+ when the blood has low pH. Low pH in the blood is due to accumulation of carbon dioxide and consequent formation of carbonic acid. Protonation of the residues cause allosteric interaction, due to ionic interaction, of the subunits hence resulting to conformation change of haemoglobin between T-state and R-state