9480
When applied to two - component systems , several research groups have shown they can be used to identify the amino acid interactions between response regulators and histidine kinases and the specificity therein .
 Chemical: amino acid; Chemical: histidine
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: amino acid; Chemical: histidine