Question

What is the fundamental difference between cation/anion exchange columns?

a. What does this difference have to do with the pI of your target protein?

b. If you run either cation/anion exchange columns with the pH equal to the target protein’s pI, what will happen?

Answer 1

What is the fundamental difference between cation/anion exchange columns?

As the name implies, the cation searches for psitively charged molecules, such as protonated amine groups in amino acids ; wheras the anion targets negativley charged molecules, such as carboxilic groups deprotonated

a. What does this difference have to do with the pI of your target protein?

pI --> isoelectric point, we search for the point in which the aminio acid has 0 charge, due to amino/carboxil groups

b. If you run either cation/anion exchange columns with the pH equal to the target protein’s pI, what will happen?

since it should not be charged, then the molecule will remain in solution, since it is not charged, will not be attracted by either column