Arginine Metabolism Revisited.

Mammalian arginine metabolism is complex due to the expression of multiple enzymes that utilize arginine as substrate and to interactions or competition between specific enzymes involved in arginine metabolism. Moreover, cells may contain multiple intracellular arginine pools that are not equally accessible to all arginine metabolic enzymes, thus presenting additional challenges to more fully understanding arginine metabolism. At the whole-body level, arginine metabolism ultimately results in the production of a biochemically diverse range of products, including nitric oxide, urea, creatine, polyamines, proline, glutamate, agmatine, and homoarginine. Included in this group of compounds are the methylated arginines (e.g., asymmetric dimethylarginine), which are released upon degradation of proteins containing methylated arginine residues. Changes in arginine concentration also can regulate cellular metabolism and function via a variety of arginine sensors. Although much is known about arginine metabolism, elucidation of the physiologic or pathophysiologic roles for all of the pathways and their metabolites remains an active area of investigation, as exemplified by current findings highlighted in this review.