And the ornithine is combined with the carbon acid or the carbon phosphate to form the citrulline. And citrulline is yet another amino acid. So ultimately, even though these two are amino acids, they're not actually used in protein synthesis. Remember, these aren't part of the 20 amino acids that our body uses to synthesize proteins. Now, once we form citrulline in step two, that moves into the cytoplasm of the cell, and in a cytoplasm, we combine the citrulline with aspartate to form argininosuxnate. Now, an important point must be made about step three.