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arginine degradation I (arginase pathway)

General Background Arginase-mediated : ARG L-arginine degradation is widely distributed in the biosphere, and is found in all primary kingdoms . The first step in this process, catalyzed by the enzyme arginase, is the hydrolysis of :ARG L-arginine to form :L-ORNITHINE L-ornithine and :UREA urea. There are many variations of the arginase pathway, since the fate of the products of the arginase reaction may be different in different organisms. Variants of arginase-based : ARG L-arginine-degradation pathways include : ARGASEDEG-PWY arginine degradation I (arginase pathway), :ARG-PRO-PWY arginine degradation VI (arginase 2 pathway), and : ARG-GLU-PWY arginine degradation VII (arginase 3 pathway). About This Pathway This variant is the "classical" arginase pathway, having the widest distribution. The pathway is found in mammals as well as many bacteria. In this pathway :ARG L-arginine is converted into :GLT L-glutamate in a series of three steps; following the initial step, catalyzed by arginase, :L-ORNITHINE L-ornithine is converted to :L-GLUTAMATE_GAMMA-SEMIALDEHYDE L-glutamate gamma-semialdehyde by :CPLX-6747 ornithine aminotransferase (OAT). :L-GLUTAMATE_GAMMA-SEMIALDEHYDE L-glutamate gamma-semialdehyde undergoes a spontaneous conversion to : L-DELTA1-PYRROLINE_5-CARBOXYLATE (S)-1-pyrroline-5-carboxylate, which is then converted in the third step, catalyzed by :CPLX-6746 Δ-1-pyrroline-5-carboxylate dehydrogenase, to :GLT L-glutamate. In a subsequent step glutamate dehydrogenase (GDH) removes the amino group from :GLT L-glutamate, generating :2-KETOGLUTARATE 2-oxoglutarate, which is fed to the :TCA TCA cycle (see : GLUTAMATE-DEG1-PWY glutamate degradation I). Such conversion into :GLT L-glutamate is a common route for the degradation of amino acids, including :GLN L-glutamine, :HIS L-histidine, and :PRO L-proline (see the pathways : GLUTAMINDEG-PWY glutamine degradation I, : HISDEG-PWY histidine degradation I and : PROUT-PWY proline degradation). In mammals, the enzymes catalyzing the reactions of this pathway are present in the mitochondrial matrix. There are two isoforms of mammalian arginases - a mitochondrial form, including the humane :CPLX-6622 arginase type 2, and a cytosolic form, which includes the human :CPLX-6621 arginase type 1. The cytosolic arginases, however, are believed to be involved mostly in the urea cycle (see : PWY-4984 urea cycle) , although this notion has been questioned . Human arginases were found in many tissues, including kidney and prostate, brain, skeletal muscle, placenta, lung, mammary gland, macrophage, uterus, testis, and gut . In prokaryotes, this pathway is used for the catabolism of : ARG L-arginine as either a carbon or a nitrogen source. Arginases have been detected in and characterized from several species, including bacilii , agrobacteria , cyanobacteria , Proteus spp. , : TAX-271 Thermus aquaticus , and mycobacteria . However, in most of these cases the fate of :L-ORNITHINE L-ornithine is not known . In some cases : ARG L-arginine can can be utilized by the organism as both carbon and nitrogen source, while in others it is used only as a nitrogen source. In addition, some organisms possess the enzyme urease, which converts the urea formed by arginase into : CARBON-MONOXIDE carbon monoxide and : AMMONIA ammonia, a favorite nitrogen source. In some strains, such as : TAX-1402 Bacillus licheniformis, the pathway is subject to strong catabolite repression during growth on glucose . In some strains, the pathway is also subject to nitrogen catabolite repression. Such regulation is species specific and is not universal . Although this pathway was not originally believed to act in plants, later studies provided evidence for its existence . For example, in : TAX-3349 Pinus sylvestris (Scots pine), this pathway appears to be required to provide the glutamate that is needed for glutamine biosynthesis during the early stages of seed germination . However, further work will be required to determine if this is the only pathway that operates in plants, or whether additional pathways such as : ARG-PRO-PWY arginine degradation VI (arginase 2 pathway) can also contribute to arginine degradation .

from BIOCYC source record: ARA_ARGASEDEG-PWY
Type: pathway
Taxonomic scope
organism-specific biosystem

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