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# Isoelectric points of proteins and exchange columns

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You have a protein that is well behaved at pH=7.0 (The ph of the buffer is 7.) and the pI of your protein is equal to 4.3 (pI=4.3). You have decided to use ion exchange chromatography to help isolate your protein.
1.Using this information, would you use a cationic column (anion exchange) or an anionic column (cation exchange)? Why?
2.What residues in your protein do you think would be in a majority?
3.Same question as in question 1 with the exception that your protein has a pI=9.2.

https://brainmass.com/biology/protein-structure-and-synthesis/isoelectric-points-of-proteins-and-exchange-columns-396216

#### Solution Preview

1) Since the pI (the pH at which the protein has 0 charge) is 4.3, when we are at pH=7, we will be generating more DEPROTONATION and thus more negative charge. So we will be generating anions, ...

#### Solution Summary

In this solution the use of the isoelectric point is explained. Also we explain how changes in the pH of the buffer containing a protein will alter its charge if we know its isoelectric point. A brief discussion of cation and anion exchange columns is also included, focusing on how to pick the correct column for the given conditions.

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