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L-Ornithine
L-Ornithin2.svg
IUPAC name
Other names (+)-(S)-2,5-Diaminovaleric acid
Identifiers
CAS number 70-26-8 Yes check.svgY
PubChem 389
EC-number 200-731-7
MeSH Ornithine
SMILES
InChI
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)
 Yes check.svgY (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 lactamization

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

  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. ^ 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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