The majority of citrulline either floats in the blood passively or is transported to the kidneys for conversion into arginine. Therefore, most bioactivities of citrulline are secondary to arginine ingestion.
Approximately 83% of orally ingested citrulline appears to be taken up by the kidneys,[1][2][3] where it is converted into L-arginine in the proximal tubules (via the enzymes arginosuccinate synthase and arginosuccinate lyase[4]); this conversion of citrulline into arginine (either from supplemental citrulline or that produced as a byproduct of arginine creation of nitric oxide) accounts for 5%–15% of circulating arginine but 60% of total arginine (the difference being due to the ability of arginine to be incorporated into proteins).[5][6]
References
- ^Interorgan amino acid exchange in humans: consequences for arginine and citrulline metabolism
- ^Intestinal and hepatic metabolism of glutamine and citrulline in humans
- ^Source and fate of circulating citrulline
- ^Levillain O, Parvy P, Hassler CAmino acid handling in uremic rats: citrulline, a reliable marker of renal insufficiency and proximal tubular dysfunction.Metabolism.(1997-Jun)
- ^Rougé C, Des Robert C, Robins A, Le Bacquer O, Volteau C, De La Cochetière MF, Darmaun DManipulation of citrulline availability in humansAm J Physiol Gastrointest Liver Physiol.(2007 Nov)
- ^Castillo L, Beaumier L, Ajami AM, Young VRWhole body nitric oxide synthesis in healthy men determined from 15N arginine-to-15Ncitrulline labeling.Proc Natl Acad Sci U S A.(1996-Oct-15)