Well, two three BPG is a molecule that is a byproduct of cellular respiration. So when cell respiration takes place inside the cells of the adult individual, they produce two three BPG. And two three BPG can actually bind into that cavity into the space that is found in the adult hemoglobin. Now, as soon as the binding takes place, when the two three BPG binds into that space inside the adult hemoglobin, it creates a change in the structure of the adult hemoglobin. And what that does is it decreases the adult hemoglobin's ability to actually bind to oxygen. It lowers its affinity for oxygen.