- Ornithine
-
L-Ornithine 
L-OrnithineOther names(+)-(S)-2,5-Diaminovaleric acid, (+)-(S)-2,5-Diaminopentanoic acidIdentifiers CAS number 70-26-8 
PubChem 6262 ChemSpider 6026 UNII E524N2IXA3 EC-number 200-731-7 DrugBank DB00129 KEGG D08302 MeSH Ornithine ChEBI CHEBI:15729 
ChEMBL CHEMBL446143 Jmol-3D images Image 1 - O=C(O)[C@@H](N)CCCN
- InChI=1S/C5H12N2O2/c6-3-1-2-4(7)5(8)9/h4H,1-3,6-7H2,(H,8,9)/t4-/m0/s1
Key: AHLPHDHHMVZTML-BYPYZUCNSA-N
InChI=1/C5H12N2O2/c6-3-1-2-4(7)5(8)9/h4H,1-3,6-7H2,(H,8,9)/t4-/m0/s1
InChI=1/C5H12N2O2/c6-3-1-2-4(7)5(8)9/h4H,1-3,6-7H2,(H,8,9)/t4-/m0/s1
Key: AHLPHDHHMVZTML-BYPYZUCNBZ
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) 
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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 that 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 not to be a part of genetic code because polypeptides containing unprotected ornithines undergo spontaneous lactamization.[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 decarboxylased, then modified greatly by Cytochrome P450.
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..
- ^ Arthur L. Weber and Stanley L. Miller (1981). "Reasons for the Occurrence of the Twenty Coded Protein Amino Acids". J. Mol. Evol. 17 (5): 273–284. doi:10.1007/BF01795749. PMID 7277510. http://physwww.mcmaster.ca/~higgsp/3D03/WeberReasons.pdf.
- ^ 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.
K→acetyl-CoA G G→pyruvate→citrateG→glutamate→
α-ketoglutarateotherα-Ketoisovaleric acid · Isobutyryl-CoA · Methacrylyl-CoA · 3-Hydroxyisobutyryl-CoA · 3-Hydroxyisobutyric acid · 2-Methyl-3-oxopropanoic acidG→fumarateG→oxaloacetatesee urea cycleOther biochemical families: prot · nucl · carb (glpr, alco, glys) · lipd (fata/i, phld, strd, gllp, eico) · amac/i · ncbs/i · ttpy/iCategories:- Basic amino acids
- Urea cycle
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