Figure 1.

Metabolism of endogenous methylarginines. N^G-monomethyl-l-arginine (NMMA), asymmetric N^G,N^G-dimethyl-l-arginine (ADMA) and symmetric N^G,N’^G-dimethyl-l-arginine (SDMA) derive upon hydrolysis of proteins methylated on arginine residues. ADMA and NMMA are further hydrolyzed to citrulline by dimethylarginine dimethylaminohydrolase (DDAH). All three endogenous methylarginines are also converted to the corresponding α-keto-derivatives by alanine:glyoxylate aminotransferase 2 (AGXT2). NMMA, ADMA and SDMA could be also N-α-acetylated, however, the enzyme, which is responsible for this reaction, is still unknown. All three endogenous methylarginines are excreted by kidneys.