And these positively charged sections of beats of a beta two and beta one subunits can bond electrostatically to the negatively charged phosphate groups of 23 BPG. And this space, this cavity inside the hemoglobin, only exists when no oxygen are actually bound to the heme groups found within our hemoglobin. So once again, note that 23 BPG can only bond to deoxiform of hemoglobin because when oxygen actually binds onto the hemoglobin, it creates a conformational change that squeezes in, that narrows in that space in the middle. And so once oxygen is actually bound to the hemoglobin and that space closes in, and the two three BPG shown in purple can no longer actually bind onto our hemoglobin. So, once again, two three BPG only binds to deoxy hemoglobin proteins found within the red blood cells. Now, once the two three BPG actually binds to our deoxy hemoglobin, it makes the protein much less likely to actually bind to other oxygen molecules.