19000
By exploiting ( 125 ) I - polyubiquitin chain formation as a functional readout of enzyme activity , we have quantitatively examined the mechanism of human E6AP / UBE3A for the first time .
 ( 125 ) I
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 ( 125 ) I