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Pathway details: superpathway of citrulline metabolism

General info Interaction details Linked pathways Protein-protein interactions
  Pathway was created on Mon Jul 29, 2013.
 Contributed by aracyc:
Supporting evidence for this pathway in Arabidopsis: This is a superpathway composed of one or more sub-pathways that may have different levels of evidence. All of its sub-pathways have been accepted for this species using SAVI v.1.0 [more info] Summary from MetaCyc: General Background citrulline is a non-standard amino acid that is not normally incorporated into proteins during protein synthesis. The name citrulline was coined in 1930 from Citrullus, the Latin name of the watermelon, from which it was first isolated. Free citrulline is formed mainly by catabolism of amino acids in the small intestine (see citrulline biosynthesis), as an intermediate in the conversion of ammonia to urea in the urea cycle, and as a by-product during the production of nitric oxide (see citrulline-nitric oxide cycle). In addition, citrulline is also formed by modification of arginine residues in proteins (see ). About This Pathway Free citrulline metabolism involves three key enzymes: nitric oxide synthase (NOS, EC, which catalyzes the production of nitric oxide from arginine, generating citrulline as a by-product, (OCT, EC, which produces citrulline by condensing carbamoyl phosphate and L-ornithine, and (ASS, EC, which converts citrulline into argininosuccinate. The tissue distribution of these enzymes results in three orthogonal metabolic routes for citrulline in mammals, all of which are depicted in this pathway: 1. In the liver, citrulline is locally synthesized by the combined action of , and , and metabolized by and back to arginine. The main purpose of this cycle is the production of urea, and it is described in greater detail in the pathway urea cycle. 2. In most of the tissues producing NO, citrulline is generated from arginine in a single step by NOS, and then recycled back into arginine via and . The main purpose of this cycle is the production of NO, and it is described in greater detail in the pathway citrulline-nitric oxide cycle. 3. In the gut citrulline is synthesized from glutamine and other amino acids (such as proline) by the combined action of many enzymes, including , , , and . Citrulline is then released into the blood, and converted back into arginine in the kidneys by and . The main purpose of this pathway is the transport of arginine in the blood, avoiding captation by the liver, and it is described in the pathway citrulline biosynthesis. Citrulline has long been administered in the treatment of inherited urea cycle disorders, and recent studies suggest that it may be used to control the production of NO. In plants, citrulline has additional roles. It has been shown that in drought-tolerant wild watermelon leaves citrulline functions both as a compatible solute and ahydroxyl radical scavenger .
  Parts of this pathway occur in: multiple locations     cytosol     plastid     nucleus     mitochondrion  

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metabolite [33]
protein complex [14]
RNA [32]
polypeptide [36]
gene [32]

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