And this is our oxalo acetate intermediate. Now, the enzyme that catalyzes this reaction is the Pyruvate, because that's the substrate carboxylase, because this is a carboxylation process. And this enzyme consists of four identical but individual subunits. Now let's talk a bit about these important regions that exist on the enzyme on these subunits. So we have two very important regions. One of these regions, known as the biotin binding domain, actually contains this molecule.