N(omega)-methyl-L-arginyl-[protein] + S-adenosyl-L-methionine => N(omega),N(omega)'-dimethyl-L-arginyl-[protein] + S-adenosyl-L-homocysteine + H(+)
n(omega)-methyl-l-arginyl-[protein] + s-adenosyl-l-methionine => n(omega),n(omega)'-dimethyl-l-arginyl-[protein] + s-adenosyl-l-homocysteine + h(+)