Well, because the carbon, well, phosphate synthetase uses the ammonia as a substrate and not ammonium. So remember, inside our body we have ammonium that exists in somewhat of an equilibrium with its ammonia. And so Ammonium transforms into ammonia and then that is used as a substrate by carbon, well phosphate synthetase to basically combine this ammonia with this carbon here, kicking off this orthophosphate. And so we form the carbonic acid and then the second ATP comes into play. And this basically attaches the phosphate here, attaches onto this oxygen to basically form the carbon oil phosphate as we have it here. And so this molecule is high in energy, it has a high transfer potential because of this anhydrate bond shown here.