Ornithine
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| Names | |
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| IUPAC name
(2S)-2,5-diaminopentanoic acid
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| Other names
(+)-(S)-2,5-Diaminovaleric acid
(+)-(S)-2,5-Diaminopentanoic acid | |
| Identifiers | |
3D model (JSmol)
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| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| DrugBank | |
| ECHA InfoCard | 100.000.665 |
| EC Number |
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| KEGG | |
| MeSH | Ornithine |
PubChem CID
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| UNII | |
CompTox Dashboard (EPA)
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| Properties[1] | |
| C5H12N2O2 | |
| Molar mass | 132.16 g/mol |
| Melting point | 140 °C (284 °F; 413 K) |
| Soluble | |
| Solubility | Soluble in ethanol |
| Acidity (pKa) | 1.94 |
Chiral rotation ([α]D)
|
+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).
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Ornithine is a non-proteinogenic α-amino acid that plays a role in the urea cycle. It is not incorporated into proteins during translation. Ornithine is abnormally accumulated in the body in ornithine transcarbamylase deficiency, a disorder of the urea cycle. The moiety derived from ornithine is called ornithyl.[2]
Role in urea cycle
[edit]L-Ornithine is one of the products of the action of the enzyme arginase on L-arginine, creating urea. Therefore, ornithine is a central component of the urea cycle, which enables the disposal of excess nitrogen. Ornithine itself is recycled and, in a sense, acts as a catalyst.
First, ammonia is converted into carbamoyl phosphate (H
2NC(O)OPO2−
3) by carbamoyl phosphate synthetase. Ornithine transcarbamylase then catalyzes the reaction between carbamoyl phosphate and ornithine to form citrulline and phosphate (Pi). Another amino group is contributed by aspartate, leading to the formation of arginine and the byproduct fumarate. The resulting arginine, a guanidinium compound, is subsequently hydrolyzed by arginase to regenerate ornithine and release urea.
The two nitrogen atoms in urea are derived from ammonia and aspartate, while the nitrogen atoms in ornithine remain unchanged.
Ornithine is not an amino acid directly coded for by DNA; that is, it is not a proteinogenic amino acid. However, in mammalian non-hepatic tissues, the primary role of the urea cycle is often the biosynthesis of arginine. As an intermediate in metabolic pathways, ornithine is thus quite important.[4]
Other reactions
[edit]Ornithine, through the action of ornithine decarboxylase (EC 4.1.1.17), serves as the starting point for the synthesis of polyamines such as putrescine.
In bacteria such as E. coli, ornithine can be synthesized from L-glutamate.[5]
Research
[edit]Exercise fatigue
[edit]L-Ornithine supplementation has been shown to attenuate fatigue in subjects in placebo-controlled studies using a cycle ergometer. The results suggest that L-ornithine may exert an antifatigue effect by increasing the efficiency of energy consumption and promoting the excretion of ammonia.[6][7]
Weightlifting supplement
[edit]Amino acid supplements, including L-ornithine, are frequently marketed to bodybuilders and weightlifters with claims of increasing levels of human growth hormone (HGH), muscle mass, and strength. A short, four-day clinical study conducted in 1993 reported that L-ornithine, in combination with L-arginine and L-lysine at 2 g/day each, did not increase HGH levels.[8] A review published in 2002 concluded, "The use of specific amino acids to stimulate GH release by athletes is not recommended."[9]
Cirrhosis
[edit]L-ornithine L-aspartate (LOLA), a stable salt of ornithine and aspartic acid, has been used in the treatment of cirrhosis[10] and hepatic encephalopathy.[11]
See also
[edit]References
[edit]- ^ CRC Handbook of Chemistry and Physics (62nd ed.). CRC Press. 1981. p. C-408.
- ^ Sivashanmugam, M (February 2017). "Ornithine and its role in metabolic diseases: An appraisal". Biomedicine & Pharmacotherapy. 86: 185–194. doi:10.1016/j.biopha.2016.12.024. PMID 27978498.
- ^ Langley DB, Templeton MD, Fields BA, Mitchell RE, Collyer CA (June 2000). "Mechanism of inactivation of ornithine transcarbamoylase by Ndelta-(N'-Sulfodiaminophosphinyl)-L-ornithine, a true transition state analogue? Crystal structure and implications for catalytic mechanism". The Journal of Biological Chemistry. 275 (26): 20012–9. doi:10.1074/jbc.M000585200. PMID 10747936.
- ^ Weber AL, Miller SL (1981). "Reasons for the occurrence of the twenty coded protein amino acids" (PDF). Journal of Molecular Evolution. 17 (5): 273–284. Bibcode:1981JMolE..17..273W. doi:10.1007/BF01795749. PMID 7277510. S2CID 27957755.
- ^ "Ornithine Biosynthesis". School of Biological and Chemical Sciences, Queen Mary, University of London. Archived from the original on 2012-04-14. Retrieved 2007-08-17.
- ^ Sugino T, Shirai T, Kajimoto Y, Kajimoto O (November 2008). "L-ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism". Nutrition Research. 28 (11): 738–743. doi:10.1016/j.nutres.2008.08.008. PMID 19083482.
- ^ Demura S, Yamada T, Yamaji S, Komatsu M, Morishita K (October 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): 1166–1171. doi:10.1038/ejcn.2010.149. hdl:2297/25434. PMID 20717126.
- ^ Fogelholm GM, Näveri HK, Kiilavuori KT, Härkönen MH (September 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.
- ^ Chromiak JA, Antonio J (2002). "Use of amino acids as growth hormone-releasing agents by athletes". Nutrition. 18 (7–8): 657–661. doi:10.1016/s0899-9007(02)00807-9. PMID 12093449.
- ^ Sikorska H, Cianciara J, Wiercińska-Drapało A (June 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 (in Polish). 28 (168): 490–495. PMID 20642112. Retrieved 10 March 2025 – via ResearchGate.
- ^ Butterworth R, McPhail M (February 2019). "L-Ornithine L-Aspartate (LOLA) for Hepatic Encephalopathy in Cirrhosis: Results of Randomized Controlled Trials and Meta-Analyses". Drugs. 79 (Suppl 1): 31–37. doi:10.1007/s40265-018-1024-1. PMC 6416237. PMID 30706425.
External links
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