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