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Pathway Description
Arginine and Proline Metabolism
Homo sapiens
Metabolic Pathway
The arginine and proline metabolism pathway illustrates the biosynthesis and metabolism of several amino acids including arginine, ornithine, proline, citrulline, and glutamate in mammals. In adult mammals, the synthesis of arginine takes place primarily through the intestinal-renal axis (PMID: 19030957). In particular, the amino acid citrulline is first synthesized from several other amino acids (glutamine, glutamate, and proline) in the mitochondria of the intestinal enterocytes (PMID: 9806879). The mitochondrial synthesis of citrulline starts with the deamination of glutamine to glutamate via mitochondrial glutaminase. The resulting mitochondrial glutamate is converted into 1-pyrroline-5-carboxylate via pyrroline-5-carboxylate synthase (P5CS). Alternately, the 1-pyrroline-5-carboxylate can be generated from mitochondrial proline via proline oxidase (PO). Ornithine aminotransferase (OAT) then converts the mitochondrial 1-pyrroline-5-carboxylate into ornithine and the enzyme ornithine carbamoyltransferase (OCT -- using carbamoyl phosphate) converts the ornithine to citrulline (PMID: 19030957). After this, the mitochondrial citrulline is released from the small intestine enterocytes and into the bloodstream where it is taken up by the kidneys for arginine production. Once the citrulline enters the kidney cells, the cytosolic enzyme argininosuccinate synthetase (ASS) will combine citrulline with aspartic acid to generate argininosuccinic acid. After this step, the enzyme argininosuccinate lyase (ASL) will remove fumarate from argininosuccinic acid to generate arginine. The resulting arginine can either stay in the cytosol where it is converted to ornithine via arginase I (resulting in the production of urea) or it can be transported into the mitochondria where it is decomposed into ornithine and urea via arginase II. The resulting mitochondrial ornithine can then be acted on by the enzyme ornithine amino transferase (OAT), which combines alpha-ketoglutarate with ornithine to produce glutamate and 1-pyrroline-5-carboxylate. The mitochondrial enzyme pyrroline-5-carboxylate dehydrogenase (P5CD) acts on the resulting 1-pyrroline-5-carboxylate (using NADPH as a cofactor) to generate glutamate. Alternately, the mitochondrial 1-pyrroline-5-carboxylate can be exported into the kidney cell’s cytosol where the enzyme pyrroline-5-carboxylate reductase (P5CR) can convert it to proline. While citrulline-to-arginine production primarily occurs in the kidney, citrulline is readily converted into arginine in other cell types, including adipocytes, endothelial cells, myocytes, macrophages, and neurons. Interestingly, chickens and cats cannot produce citrulline via glutamine/glutamate due to a lack of a functional pyrroline-5-carboxylate synthase (P5CS) in their enterocytes (PMID: 19030957).
References
Arginine and Proline Metabolism References
Lehninger, A.L. Lehninger principles of biochemistry (4th ed.) (2005). New York: W.H Freeman.
Salway, J.G. Metabolism at a glance (3rd ed.) (2004). Alden, Mass.: Blackwell Pub.
Wu G, Bazer FW, Davis TA, Kim SW, Li P, Marc Rhoads J, Carey Satterfield M, Smith SB, Spencer TE, Yin Y: Arginine metabolism and nutrition in growth, health and disease. Amino Acids. 2009 May;37(1):153-68. doi: 10.1007/s00726-008-0210-y. Epub 2008 Nov 23.
Pubmed: 19030957
Wu G, Morris SM Jr: Arginine metabolism: nitric oxide and beyond. Biochem J. 1998 Nov 15;336 ( Pt 1):1-17. doi: 10.1042/bj3360001.
Pubmed: 9806879
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