19511
Two of the 5 natural cysteines , Cys27 and Cys219 , are essential for enzymatic activity and form a disulfide bridge .
 Chemical: cysteines; Chemical: disulfide
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: cysteines; Chemical: disulfide