|Jmol-3D images||Image 1|
|Molar mass||132.16 g/mol|
|Melting point||140 °C; 284 °F; 413 K|
|Solubility in water||soluble|
|Solubility||soluble in ethanol|
|Chiral rotation [α]D||+11.5 (H2O, c = 6.5)|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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.
Potential medical uses
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.
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.
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- 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.
- Ornithine Biosynthesis. School of Biological and Chemical Sciences, Queen Mary, University of London. Retrieved 2007-08-17.
- Sugino, T; Shirai, T; Kajimoto, Y; Kajimoto, O (2008). "L-ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism". Nutrition research 28 (11): 738–43. doi:10.1016/j.nutres.2008.08.008. PMID 19083482.
- Demura, S; Yamada, T; Yamaji, S; Komatsu, M; Morishita, K (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): 1166–71. doi:10.1038/ejcn.2010.149. PMID 20717126.
- Sikorska, H; Cianciara, J; Wiercińska-Drapało, A (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 : organ Polskiego Towarzystwa Lekarskiego 28 (168): 490–5. PMID 20642112.
- Fogelholm et al.; Näveri, HK; Kiilavuori, KT; Härkönen, MH (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. PMID 8220394.