Allosteric Effects
Bisphosphoglycerate (BPG) cannot bind to the oxygenated R state of hemoglobin because

BPG binds to the R state with the same affinity as the T state
its binding pocket becomes too small to accommodate BPG
it is displaced from the heme by movement of the proximal histidine
it is displaced from the heme by oxygen

ANSWER DOWNLOAD EXAMIANS APP