18785
Tryptophan hydroxylase ( TPH ) is the rate - limiting enzyme in 5 - HT synthesis , and the recent identification of a second , neuron - specific TPH isoform ( TPH2 ) opened up a new area of research .
 Tryptophan, 5 - HT
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Tryptophan, 5 - HT