Here we're going to say that reaction 2 of Phase B of the urea cycle is dealing with condensation. Here, citrulline undergoes condensation with aspartate to produce arginosuccinate. Now, this is catalyzed by the enzyme arginosuccinate synthetase. Again, remember, energy is being used in order to do this where we have molecules that are mingling together, so synthetase is the class of enzyme required. The name itself, remember, is the substrate followed by the class of enzyme.
Now, in this process, 1 ATP is hydrolyzed to 1 AMP and 2 inorganic phosphates. This is equivalent to saying you have 2 ATP becoming 2 ADP. If we take a look here, we have our citrulline, it gained this carbamoyl group from our ornithine molecule in reaction 1. Here, we have our aspartate. We utilize ATP in order to produce AMP and 2 inorganic phosphates. We have our enzyme that's being utilized. We're going to say as a result of this, we're going to create our connection of arginine to arginosuccinate. Basically, we're going to have this carbon here single-bonding itself to nitrogen. Nitrogen here, ideally wants to make 3 bonds in order to stay neutral, so it's just going to be an NH group. This represents our argininosuccinate group.
Then here, succinate, remember, itself, is the deprotonated form, the part that the carboxylic acids have given away the H+. It's a dicarboxylic acid that has given away its 2 acidic hydrogens. So we have 2 carboxylate ends here. This represents our succinate molecule.