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. And to actually be able to catalyze this reaction, that histidine has to be modified with the addition of a phosphoryl group. And to see what we mean, let's take a look at these two steps. So in step one, we basically have this enzyme.