12978
We demonstrate , using mass spectrometry and X - ray crystallography , that the selective inhibitor covalently modifies PI3K alpha on cysteine 862 ( C862 ) , an amino acid unique to the alpha isoform , and that PI3K beta , - gamma , and - delta are not covalently modified .
 Chemical: cysteine; Chemical: amino acid
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: cysteine; Chemical: amino acid