Posttranslational modifications (PTMs) of arginine that occur within proteins and have been detected in vivo. MMA = Monomethylarginine, SDMA = Symmetric dimethylarginine, ADMA = Asymmetric dimethylarginine, MG-H1 = 5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine, CEA = Carboxyethylarginine, CMA = Carboxymethylarginine.