So a molecule known as two three biphosphoglycerate, or simply two three BPG can bind to hemoglobin at a specific allosteric site at low oxygen concentrations. And by binding to our hemoglobin, what the two three BPG essentially does is it decreases definitive to our oxygen molecules by basically changing the three dimensional shape of hemoglobin. Now, why in a world when our two three BPG want to actually lower the activity of hemoglobin for oxygen? Well, at low concentrations of oxygen, we basically want to make sure that all the oxygen ends up in our tissues of the body. So that means we do not want our hemoglobin to actually bind that oxygen very strongly. And that's exactly why, at low concentrations of oxygen, that two, three BPG binds to the allosteric side of hemoglobin.