An amino acid not used in protein made by the urea cycle.

This exists primarily in the liver. It also exists plentifully in plant foods such as onion and garlic. It is used for detoxification of ammonia and in the treatment of fatigue.

is an amino acid that supports the body in optimizing blood flow through its conversion to L-arginine and then nitric oxide (NO).

The chemical compound citrulline is an α-amino acid (AA). Its name is derived from citrullus, the Latin word for watermelon, from which it was first isolated.