16042
A new study shows that , upon serine starvation , the tumor suppressor p53 activates p21 to shift metabolic flux from purine biosynthesis to glutathione production , which enhances cellular proliferation and viability by combating ROS ( Maddocks et al . , 2013 ) .
 Chemical: serine; Chemical: purine; Chemical: glutathione
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities: serine, purine, glutathione 
Answer:
 Chemical: serine; Chemical: purine; Chemical: glutathione