So in that discussion, we mentioned that two, three BPG is actually an intermediate in the process of glycolysis. And two, three BPG can basically affect the affinity of hemoglobin for oxygen. Now, what exactly is the function of two three BPG in this reaction? So we see that this reaction doesn't actually take place in a single step because it involves the presence of a catalytic amount of two, three bisphosphoglyceride. And what it does is it basically plays the role of maintaining, so keeping that catalytic histidine amino acid in its activosphorylated form inside the active side of the phosphoglycerate mutate. So basically, if we look at the active side of this mutase, we'll see a catalytic residue, a histidine.