Now, what happens in the presence of two, three BPG? Well, two, three BPG is a relatively small molecule that contains many negative charges. And this molecule is small enough to actually fit inside that positively charged pocket found at the center of the deoxy hemoglobin in the T state. And by going into that pocket, the negative charges of this two three PPG can interact with the positive charges of the residues found on the beta one and the beta two subunits. And if we zoom in on this interaction so this black molecule is the two, three BPG. If we zoom in on this molecule, this is what we get.