Could anyone please help me explain why the answer is E ?

[Nam Ly]

If you want to perform an anion-exchange purification of a protein which has a pI of 7.5, what pH will you choose for this experiment ?

A. pH 6.0
B. pH 7.0
C. pH 7.5
D. pH 8.0
E. pH 9.0

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[Dr. Meliodas]

If you want to perform an anion-exchange purification of a protein which has a pI of 7.5, what pH will you choose for this experiment ?

A. pH 6.0
B. pH 7.0
C. pH 7.5
D. pH 8.0
E. pH 9.0

You want the protein to have a negative charge because your are doing anion-exchange (so you are trying to isolate anions/negative charge). The fact that the pI is slightly more basic means that the protein is normally slightly positively charged. So to make it a negative charge you want a more basic pH thus 9.0

 

[Nam Ly]

Thank you very much!