N(alpha),N(alpha)-dimethyl-L-tryptophan + S-adenosyl-L-homocysteine + H(+) => N(alpha)-methyl-L-tryptophan + S-adenosyl-L-methionine
n(alpha),n(alpha)-dimethyl-l-tryptophan + s-adenosyl-l-homocysteine + h(+) => n(alpha)-methyl-l-tryptophan + s-adenosyl-l-methionine