19543
The stimulation occurs in two steps , with approximately eightfold stimulation by N - terminal cleavage , approximately fourfold stimulation by C - terminal cleavage , and 23 - fold stimulation by the cleavage of both termini , compared to the pro - form with both the N - and C - terminal pro - sequences .
 N, C, N, C
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 N, C, N, C