PRMT: The post-translational methylation of arginyl residues is catalyzed by a family of enzymes called protein arginine methyltransferases (PRMTs). Nine human PRMT isoforms are capable of forming monomethylarginine (MMA), asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) on targeted proteins. Type I PRMTs form MMA and ADMA, and represent the majority of identified PRMTs. Type III enzymes, such as PRMT7, only produce MMA. Like the type I and III enzymes, type II PRMTs catalyze monomethylation; however, a second round of turnover results in the biologically distinct SDMA. A fourth type, Type IV, which results in the monomethylation of the internal guanidino nitrogen, has also been identified in yeast, but no mammalian homologue has been identified. (1)

Reference
1. Morales Y, Cáceres T, May K, Hevel JM.Biochemistry and regulation of the protein arginine methyltransferases (PRMTs). Arch Biochem Biophys.2016;590;52-138 PMID: 26612103.