21558
In all previously known haloalkane dehalogenases , these residues are either a pair of tryptophans or a tryptophan - asparagine pair .
 haloalkane, tryptophans, tryptophan, asparagine
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 haloalkane, tryptophans, tryptophan, asparagine