1434
Modeling the structure and proton transfer pathways of the mutant His - 107 - Tyr of human carbonic anhydrase II .
 Chemical: His; Chemical: Tyr
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: His; Chemical: Tyr