Alanine is one of the 21 amino acids necessary for synthesis of proteins. To begin the synthesis of arginine, oxoglutaric acid is obtained from the citric acid cycle. The oxoglutaric acid is then either processed by aspartate aminotransferase in the mitochondrion, or alanine transaminase elsewhere in the cell, in order to produce L-glutamic acid. L-glutamic acid can then be convereted to N-acetyl-L-glutamic acid by an amino acid N-acetyltransferase, which is a potential end product for this pathway. Otherwise, it can be converted reversibly by a glutamate dehydrogenase into oxoglutaric acid once again, as well as ammonia, which then becomes the product of interest. Ammonia can be converted into L-glutamine by glutamine synthetase with the addition of L-glutamic acid, and L-glutamine can be converted back to ammonia by glutaminase a. Ammonia can also be converted into carbamoyl phosphate by carbamoyl-phosphate synthase 1 in the mitochondrion, and carbamoyl phosphate can both come from and be used in both nitrogen metabolism and pyrimidine metabolism. In addition to those, it can be converted, along with ornithine, by ornithine carbamoyltransferase, also in the mitochondrion, to citrulline. Citruline, along with L-aspartic acid from the aspartate metabolism pathway, are converted by argininosuccinate synthase to argininosuccinic acid. The argininosuccinic acid is then converted by argininosuccinate lyase to fumaric adic, and L-arginine, the main product of this pathway. The fumaric acid produced can be used in the citrate cycle, while the L-arginine can be used in arginine metabolism, or can be converted by arginase to both urea and ornithine. Urea is then moved through a urea transporter out of the cell and excreted, while ornithine is used in the previously mentioned reaction to produce citrulline. Finally citrulline can be directly converted to and from L-arginine by nitric oxide synthase, and L-arginine along with ornithine can be used in D-arginine and D-ornithine metabolism.

Arginine Biosynthesis References