An amino acid, C5H12N2O2, not found in proteins, formed by hydrolyzing arginine and important in the formation of urea.
[ornith(uric acid), an acid found in birds' urine (ORNITH(O)- + URIC ACID) + -INE2.]
ornithine
Dictionary:
or·ni·thine (ôr'nə-thēn')  |
n.
An amino acid, C5H12N2O2, not found in proteins, formed by hydrolyzing arginine and important in the formation of urea.
An amino acid, C5H12N2O2, not found in proteins, formed by hydrolyzing arginine and important in the formation of urea.
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| Chemistry Dictionary: ornithine |
Variant: Orn
An amino acid, H2N(CH2)3CH(NH2)COOH, that is not a constituent of proteins but is important in living organisms as an intermediate in the reactions of the urea cycle and in arginine synthesis.
| Food and Nutrition: ornithine |
An amino acid that occurs as a metabolic intermediate in the synthesis of urea, but not involved in protein synthesis, so of no nutritional importance.
| Dental Dictionary: ornithine |
n
An amino acid, not a constituent of proteins, that is produced as an important intermediate substance in the urea cycle.
| Sports Science and Medicine: ornithine |
An amino acid produced in the liver during the formation of urea from ammonia.
| Veterinary Dictionary: ornithine |
An amino acid obtained from arginine by the action of the enzyme arginase which also splits off urea; it is an intermediate in urea biosynthesis.
- o. carbamoyl transferase (OCT), o. transcarbamoylase — see ornithine carbamoyl transferase.
- o. cycle — alternative name for urea cycle since ornithine is the carrier of the nitrogens.
- o. decarboxylase test — a means of identifying different members of the Enterobacteriaceae as well as other gram-negative bacteria.
- o.-δaminotransferase — deficiency see gyrate atrophy.
| Wikipedia: Ornithine |
| L-Ornithine | |
|---|---|
 |
|
| IUPAC name |
L-Ornithine
|
| Other names | (+)-(S)-2,5-Diaminovaleric acid |
| Identifiers | |
| CAS number | 70-26-8  |
| PubChem | 389 |
| EC-number | 200-731-7 |
| MeSH | Ornithine |
| SMILES |
C(CC(C(=O)O)N)CN
|
| InChI |
1/C5H12N2O2/c6-3-1-2-4(7)5(8)9/h4H,1-3,6-7H2,(H,8,9)/t4-/m0/s1
|
| ChemSpider ID | 6026 |
| Properties[1] | |
| Molecular formula | C5H12N2O2 |
| Molar mass | 132.16 g/mol |
| Melting point |
140 ºC |
| Solubility in water | soluble |
| Chiral rotation [α]D | +11.5 (H2O, c = 6.5) |
| (what is this?) (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
|
| Infobox references | |
Ornithine is an amino acid which plays a role in the urea cycle.
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), which creates one half of urea. 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, and, in that sense, is not involved in protein synthesis. 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. It is believed to not be a part of genetic code because polypeptides containing unprotected ornithines undergo spontaneous lactamization.
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.[2]
References
- ^ 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.
- ^ Ornithine Biosynthesis, School of Biological and Chemical Sciences, Queen Mary, University of London, http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/AminoAcid/Orn.html, retrieved 2007-08-17.
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