Definition
A non-essential and nonprotein amino acid, ornithine is critical for the production of the body's proteins, enzymes and muscle tissue. Ornithine plays a central role in the urea cycle and is important for the disposal of excess nitrogen (ammonia). Ornithine is the starting point for the synthesis of many polyamines such as putrescine and spermine. Ornithine supplements are claimed to enhance the release of growth hormone and to burn excess body fat. Ornithine is necessary for proper immune function and good liver function.; AF112968; 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 ? (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.; ORNT1). Mutations in the mitochondrial ornithine transporter result in hyperammonemia, hyperornithinemia, homocitrullinuria (HHH) syndrome, a disorder of the urea cycle. (PMID 16256388) The pathophysiology of the disease may involve diminished ornithine transport into mitochondria, resulting in ornithine accumulation in the cytoplasm and reduced ability to clear carbamoyl phosphate and ammonia loads. (OMIM 838970); Ornithine is an amino acid produced in the urea cycle by the splitting off of urea from arginine. It is a central part of the urea cycle, which allows for the disposal of excess nitrogen. L-Ornithine is also a precursor of citrulline and arginine. In order for ornithine produced in the cytosol to be converted to citrulline, it must first cross the inner mitochondrial membrane into the mitochondrial matrix where it is carbamylated by ornithine transcarbamylase. This transfer is mediated by the mitochondrial ornithine transporter (SLC25A15; Ornithine is an amino acid which plays a role in the urea cycle.
Description
Ornithine is an amino acid produced in the urea cycle by the splitting off of urea from arginine. It is a central part of the urea cycle, which allows for the disposal of excess nitrogen. L-Ornithine is also a precursor of citrulline and arginine. In order for ornithine produced in the cytosol to be converted to citrulline, it must first cross the inner mitochondrial membrane into the mitochondrial matrix where it is carbamylated by ornithine transcarbamylase. This transfer is mediated by the mitochondrial ornithine transporter (SLC25A15; AF112968; ORNT1). Mutations in the mitochondrial ornithine transporter result in hyperammonemia, hyperornithinemia, homocitrullinuria (HHH) syndrome, a disorder of the urea cycle. The pathophysiology of thef the disease may involve diminished ornithine transport into mitochondria, resulting in ornithine accumulation in the cytoplasm and reduced ability to clear carbamoyl phosphate and ammonia loads. (OMIM 838970). (A3420).
Ornithine Health Effects
General Information
- Metabolism: Ornithine undergoes extensive metabolism in the liver to L-arginine, polyamines, and proline, and several other metabolites.
- Uses/Sources: Used for nutritional supplementation, also for treating dietary shortage or imbalance. It has been claimed that ornithine improves athletic performance, has anabolic effects, has wound-healing effects, and is immuno-enhancing.
- Health Effects: Chronically high levels of ornithine are associated with at least 9 inborn errors of metabolism including: Cystathionine Beta-Synthase Deficiency, Hyperornithinemia with gyrate atrophy, Hyperornithinemia-hyperammonemia-homocitrullinuria syndrome, Hyperornithinemia-hyperammonemia-homocitrullinuria syndrome, Hyperprolinemia Type II, Lysinuric Protein Intolerance, Ornithine Aminotransferase Deficiency, Ornithine Transcarbamylase Deficiency and Prolinemia Type II.
- Route of Exposure: Absorbed from the small intestine via a sodium-dependent active transport process
Toxicity
- Carcinogenicity: No indication of carcinogenicity to humans (not listed by IARC).
- Toxicity: Oral, rat LD<sub>50</sub> = 10000 mg/kg
Mechanism of Action
| Target Name | Mechanism of Action | References |
|---|---|---|
|
High affinity cationic amino acid transporter 1 Cationic amino acid transporter 4 Cationic amino acid transporter 3 Low affinity cationic amino acid transporter 2 Glycine amidinotransferase, mitochondrial Arginase-2, mitochondrial Ornithine carbamoyltransferase, mitochondrial Ornithine aminotransferase, mitochondrial Arginase-1 Ornithine decarboxylase antizyme 1 Mitochondrial ornithine transporter 2 Mitochondrial ornithine transporter 1 Ornithine decarboxylase antizyme 2 Ornithine decarboxylase antizyme 3 |
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