Figure 2.

The arginine metabolic pathway showing the conversion of l-arginine to the neurotransmitter, nitric oxide (NO), and l-citrulline, by nitric oxide synthase (NOS), of which there are three isoforms; the conversion of l-arginine to agmatine by arginine decarboxylase (ADC), which is then converted to polyamines such as putrescine, spermidine, and spermine by agmatinase and ornithine decarboxylase (ODC); and the conversion of l-arginine to l-ornithine by arginase, which is then converted to the same polyamines. Glutamate is one of the end products of l-arginine, and glutamate serves as a precursor for the synthesis of GABA. Reproduced from Smith et al. (82) with permission from Elsevier.