Asparagine is one of the 20 most common natural amino acids on Earth. Asparagine is closely related to aspartic acid. It is an important constituent in many plant proteins. In the liver,asparagine is involved converting one amino acid to another. Asparagine helps maintain an equilibrium of the central nervous system and has therapeutic properties, but is toxic when used in excess. It is most commonly found in poultry, dairy, eggs, and beef. A byproduct of the breakdown of asparagine (asparagine-amino-succinic-acid monoamide) is also blamed for the smell in some people's urine after they have eaten asparagus. (Some scientists disagree and implicate other substances in the smell, especially methyl mercaptan.)