IUPAC name
Other names
(+)-(S)-2,5-Diaminovaleric acid, (+)-(S)-2,5-Diaminopentanoic acid
70-26-8 YesY
3D model (Jmol) Interactive image
ChEMBL ChEMBL446143 YesY
ChemSpider 6026 YesY
DrugBank DB00129 N
ECHA InfoCard 100.000.665
EC Number 200-731-7
KEGG D08302 YesY
MeSH Ornithine
PubChem 389
Molar mass 132.16 g/mol
Melting point 140 °C (284 °F; 413 K)
Solubility soluble in ethanol
Acidity (pKa) 1.94
+11.5 (H2O, c = 6.5)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Ornithine is a non proteinogenic amino acid that plays a role in the urea cycle. Ornithine is abnormally accumulated in the body in ornithine transcarbamylase deficiency. The radical is ornithyl.

Role in urea cycle

L-Ornithine is one of the products of the action of the enzyme arginase on L-arginine, creating urea. Therefore, ornithine is a central part of the urea cycle, which allows for the disposal of excess nitrogen. Ornithine is recycled and, in a manner, is a catalyst. First, ammonia is converted into carbamoyl phosphate (H
). Ornithine is converted into a urea derivative at the δ (terminal) nitrogen by carbamoyl phosphate synthetase. Another nitrogen is added from aspartate, producing the denitrogenated fumarate, and the resulting arginine (a guanidinium compound) is hydrolysed back to ornithine, producing urea. The nitrogens of urea come from the ammonia and aspartate, and the nitrogen in ornithine remains intact.

Ornithine lactamization

Ornithine is not an amino acid coded for by DNA, that is, not proteinogenic. However, in mammalian non-hepatic tissues, the main use of the urea cycle is in arginine biosynthesis, so, as an intermediate in metabolic processes, ornithine is quite important.[2]

Other reactions

Ornithine, via the action of ornithine decarboxylase (E.C., is the starting point for the synthesis of polyamines such as putrescine.

In bacteria, such as E. coli, ornithine can be synthesized from L-glutamate.[3]

Ornithine is also the starting point for cocaine biosynthesis, when decarboxylated, then modified greatly by cytochrome P450.

Potential medical uses

Exercise fatigue

L-Ornithine supplementation attenuated fatigue in subjects in a placebo-controlled study using a cycle ergometer. The results suggested that L-ornithine has an antifatigue effect in increasing the efficiency of energy consumption and promoting the excretion of ammonia.[4][5]

Weightlifting supplement

Amino acid supplements, including L-ornithine, are frequently marketed to bodybuilders and weightlifters through the claim that it will increase levels of human growth hormone (HGH). However, clinical study has shown that these supplements do not increase levels of HGH with low dose (2 grams per day divided into two doses) supplementation.[6]


L-Ornithine L-aspartate (LOLA), a stable salt of ornithine and aspartic acid, has been used in the treatment of cirrhosis.[7]


  1. Weast, Robert C., ed. (1981). CRC Handbook of Chemistry and Physics (62nd ed.). Boca Raton, FL: CRC Press. p. C-408. ISBN 0-8493-0462-8.
  2. Weber, Arthur L.; Miller, Stanley L. (1981). "Reasons for the Occurrence of the Twenty Coded Protein Amino Acids" (PDF). J. Mol. Evol. 17 (5): 273–284. doi:10.1007/BF01795749. PMID 7277510.
  3. "Ornithine Biosynthesis". School of Biological and Chemical Sciences, Queen Mary, University of London. Retrieved 2007-08-17.
  4. Sugino, T.; Shirai, T.; Kajimoto, Y.; Kajimoto, O. (2008). "L-ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism". Nutrition research. 28 (11): 738–43. doi:10.1016/j.nutres.2008.08.008. PMID 19083482.
  5. Demura, S.; Yamada, T.; Yamaji, S.; Komatsu, M.; Morishita, K. (2010). "The effect of L-ornithine hydrochloride ingestion on performance during incremental exhaustive ergometer bicycle exercise and ammonia metabolism during and after exercise". European journal of clinical nutrition. 64 (10): 1166–71. doi:10.1038/ejcn.2010.149. PMID 20717126.
  6. Fogelholm, G. M.; Näveri, H. K.; Kiilavuori, K. T.; Härkönen, M. H.; et al. (1993). "Low-dose amino acid supplementation: no effects on serum human growth hormone and insulin in male weightlifters". International Journal of Sport Nutrition. 3 (3): 290–297. doi:10.1123/ijsn.3.3.290. PMID 8220394.
  7. Sikorska, H.; Cianciara, J.; Wiercińska-Drapało, A. (2010). "Physiological functions of L-ornithine and L-aspartate in the body and the efficacy of administration of L-ornithine-L-aspartate in conditions of relative deficiency". Polski merkuriusz lekarski: organ Polskiego Towarzystwa Lekarskiego. 28 (168): 490–5. PMID 20642112.
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