3680
Transfection of cells with the dominant negative mutant of ubiquitin Ub - K48R , which prevents the formation of Lys48 - linked polyubiquitin chains , abolishes PKC - stimulated OAT1 ubiquitination and internalization .
 Lys48
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Lys48