And inside the active side of the enzyme, we have the histadine that has been modified by the addition of the phosphoryl group. And so in step one of this reaction, what happens is this three phosphorylycerate moves into the active side, and in step one, this molecule, the enzyme, transfers this phosphoryl group from the histidine of that enzyme onto the second position of this molecule. So essentially, we attach this phosphoryl group onto carbon number two, and we form the two three by or bisphosphoglycerate. And so we form this enzyme that does not contain the modified histidine, as well as a two, three BPG. Now, this two, three BPG is only present in very small amounts. Why?