4-methylamino-L-phenylalanine + S-adenosyl-L-methionine <=> 4-dimethylamino-L-phenylalanine + S-adenosyl-L-homocysteine + H(+)
4-methylamino-l-phenylalanine + s-adenosyl-l-methionine <=> 4-dimethylamino-l-phenylalanine + s-adenosyl-l-homocysteine + h(+)