Ornithine
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| Names | |
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| IUPAC name
L-Ornithine
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| Other names
(+)-(S)-2,5-Diaminovaleric acid, (+)-(S)-2,5-Diaminopentanoic acid
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| Identifiers | |
70-26-8  |
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| ChEBI | CHEBI:15729  |
| ChEMBL | ChEMBL446143 |
| ChemSpider | 6026 |
| DrugBank | DB00129 |
| EC Number | 200-731-7 |
| 725 | |
| Jmol 3D model | Interactive image |
| KEGG | D08302 |
| MeSH | Ornithine |
| PubChem | 389 |
| UNII | E524N2IXA3 |
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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 |
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Chiral rotation ([α]D)
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+11.5 (H2O, c = 6.5) |
| Vapor pressure | {{{value}}} |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 verify (what is ?) |
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| 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.
Contents
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 (phosphate-CONH2). Ornithine is converted into a urea derivative at the δ (terminal) nitrogen by carbamoyl phosphate. 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 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. 4.1.1.17), 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]
Cirrhosis
L-Ornithine L-aspartate (LOLA), a stable salt of ornithine and aspartic acid, has been used in the treatment of cirrhosis.[6]
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.[7]
References
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