6862
Analogous to the active site of Zn ( 2 + ) carboxypeptidases , calnuc has two high affinity ( K ( d ) ~ 20 nm ) , well conserved Zn ( 2 + ) - binding sites near its N terminus , although it is inactive as a peptidase .
 Zn ( 2 + ), Zn ( 2 + ), N
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Zn ( 2 + ), Zn ( 2 + ), N