5184
While uptake of Fe ( 3 + ) via the Tf mechanism is well understood , uptake of Mn ( 3 + ) via this mechanism has not been systematically studied .
 Fe ( 3 + ), Mn ( 3 + )
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Fe ( 3 + ), Mn ( 3 + )