And it's the R state that becomes very likely to bind oxygen. And that's exactly why the pure hemoglobin has a very high affinity for oxygen. And that's exactly why the black curve is to the left with respect to that blue curve. 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.