Figure 1: Arginine Metabolic Pathways: Arginine residues in intact proteins are methylated by protein arginine methyl transferases (PRMT) in to protein-bound NGmonomethyl-L-arginine (NMMA), NGNGdimethylarginine (ADMA) and NGN’Gdimethylarginine (SDMA). Upon proteolysis, free NMMA, SDMA and ADMA are released into circulation. Both ADMA and NMMA are inhibitors of endothelial nitric oxide synthase (eNOS) - which synthesizes Nitric oxide – a potent vasoprotector from free arginine. ADMA is degraded to citrulline by dimethylarginine dimethyl aminohydrolase (DDAH) in the kidneys. The chemical structures of arginine metabolites are depicted.