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Taking advantage of the strong affinity between the two split intein fragments , we devised a streamlined procedure for the purification and generation of protein alpha - thioesters from cell lysates and applied this strategy for the semisynthesis of a variety of proteins including an acetylated histone and a site - specifically modified monoclonal antibody .
 alpha - thioesters
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 alpha - thioesters