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L-arginine biosynthesis IV (archaebacteria)

General Background Arginine biosynthesis is notable for its complexity and variability at the genetic level, and by its connection with several other pathways, such as pyrimidine and polyamine biosynthesis, and certain degradative pathways. The initial steps of the arginine biosynthetic pathways proceed via N-acetylated intermediates. The presumed reason for this is that the acetylation prevents the spontaneous cyclization of glutamate derivatives, which leads to proline biosynthesis, thus keeping the two pathways separate |CITS: [12633501]|. A variation of the pathway found in some archaebacteria and hyperthermophilic bacteria utilizes a dedicated carrier protein to protect the intermediates instead of acetylation. Several alternative arginine biosynthetic pathways have evolved in bacteria: In |FRAME:ARGSYN-PWY|, which is not very common, the key intermediate |FRAME:ACETYL-GLU| (NAG) is formed by the enzyme |FRAME: EC-|. A second key intermediate downstream, |FRAME:N-ALPHA-ACETYLORNITHINE|, is hydrolyzed by the enzyme |FRAME: EC-|, releasing acetate, and forming the arginine precursor |FRAME:L-ORNITHINE|. In |FRAME:ARGSYNBSUB-PWY|), which is found in most of the prokaryotic and eukaryotic microbes investigated up to now, the two reactions mentioned above are linked: the acetyl group which is removed from |FRAME:N-ALPHA-ACETYLORNITHINE| is recycled onto glutamate, regenerating |FRAME:ACETYL-GLU| (NAG). This recycling is performed by the enzyme |FRAME: EC-|. This pathway is considered more evolved, since the overall reaction is energetically more favorable |CITS: [3534538]|. The variant |FRAME: PWY-5154| is found in several eubacteria. While in the two pathways mentioned above |FRAME:N-ALPHA-ACETYLORNITHINE| is deacetylate to |FRAME:L-ORNITHINE|, which is subsequntly transcarbamoylated to form |FRAME: L-CITRULLINE|, in this variant |FRAME:N-ALPHA-ACETYLORNITHINE| is not deacetylated. Instead, it is transcarbamoylated directly by the enzyme |FRAME: EC-|, resulting in |FRAME: CPD-7224|. The enzyme |FRAME:ACETYLORNDEACET-CPLX| can accept |FRAME: CPD-7224| as a substrate, and deacetylates it into |FRAME: L-CITRULLINE| |CITS: [16585758]|. The variant |FRAME: PWY-7400|, which has been described in the archaebacterium |FRAME: TAX-2285|, involves early intermediates that are protected not by acetylation but by a carrier protein (the LysW |FRAME: LysW|), which participates in the biosynthesis of both |FRAME: ARG| and |FRAME: LEU| in these organsims |CITS: [23434852]|. About This Pathway The linear pathway of arginine biosynthesis has been described in several organisms including the Enterobacteriaceae |CITS: [3534538]|, the |FRAME:TAX-641| |CITS: [10692366]|, and the Gram-negative bacterium |FRAME:TAX-34| |CITS: [ 9829957]|. The pathway in these organisms starts with the acetylation of the amino moiety of |FRAME: GLT| catalyzed by ArgA, ArgJ or both, yielding |FRAME:ACETYL-GLU| (NAG). Some archaeal spieces, such as |FRAME: TAX-2284|, which are known to produce |FRAME: ARG|, do not have either ArgA and ArgJ orthologs. Instead, these organisms use the |FRAME: G-17812|-encoded ligase to bind |FRAME: GLT| to a dedicated |FRAME: LysW "carrier protein"| encoded by the lysW gene. The carrier protein, as well as the next 4 enzymes in the pathway, are bifunctional and participate in both |FRAME: ARG| and |FRAME: LEU| biosynthesis in these organisms (see |FRAME: PWY-3081|). The C-terminal part of the carrier protein is acidic and is easily recognized by the subsequent enzymes, all of which have a basic environment around their active sites. In this way the subsequent transformations leading to |FRAME: L-ORNITHINE| occur while the amino acid is attached to LysW |CITS: [19620981]|. Once formed, the ornithine is removed from the carrier protein by a dedicated enzyme encoded by the |FRAME: G-17816| gene |CITS: [23434852]|.

from BIOCYC source record: META_PWY-7400
Type: pathway
Taxonomic scope
conserved biosystem

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