Now let's talk about this enzyme. So we essentially have a CO2 molecule that is attached onto the Pyruvate to form the oxyloacetate. In the process, we hydrolyzed the ATP into orthophosphen ATP and we also form two H plus ions. 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.