Asymmetric arginine methylation and structure of AMI1. A, Reaction catalyzed by PRMT6. L-arginine is converted to (asymmetric) ω-NG,NG-dimethyl-L-arginine by substitution of two hydrogen atoms with two methyl groups in a two step reaction. ω-NG-monomethyl-L-arginine is the intermediate. B, Structure of AMI1. Standard name: disodium 7,7'-(carbonyldiimino)-bis(4-hydroxy-2-naphthalenesulfonate), Mw: 548.45.