Hydrolyzes N(G),N(G)-dimethyl-L-arginine (ADMA) and N(G)-monomethyl-L-arginine (MMA) which act as inhibitors of NOS. Has therefore a role in the regulation of nitric oxide generation. H2O + N(omega),N(omega)-dimethyl-L-arginine = dimethylamine + L-citrulline Translocates from cytosol to mitochondrion upon IL-1beta stimulation in chondrocytes. Detected in heart, placenta, lung, liver, skeletal muscle, kidney and pancreas, and at very low levels in brain. Belongs to the DDAH family.