1. Basic Concepts - Nitrogen

Nitrogen (N) is a colorless, odorless, tasteless, and mostly inert, ubiquitous elemental gas constituting 78 % by volume of Earth's atmosphere. Many biologically substances, such as ammonia, amino acids and proteins, nucleic acids (both RNA and DNA), nitric oxide, and neurotransmitters contain nitrogen constituting about 3 % by weight of nitrogen.

Protein derived from food is a major source of excess nitrogen. Thus food intake has an impact on the ammonia levels of patients with deficiencies in ammonia metabolism.

Figure 1 illustrates the inter-organ flow of metabolites in nitrogen metabolism (Based on Rabier D. 2007—Ref 1)