the human enzyme required a reducing system , ascorbic acid and methylene blue , for maximal activity and was able to oxidize d-tryptophan , 5-hydroxy-l-tryptophan as well as l-tryptophan , but kinetic studies indicated that the best substrate of the enzyme was l-tryptophan .
C0000578
5-hydroxy-l-tryptophan
C0041249
l-tryptophan