[jena]

Hi,

My Question:

Given a cation exchange column, which pH is the most suitable for testing the purity of a protein(pI=8)

a. pH=9
b. pH=6
c. pH=0.5

I think the answer is c, because pH<pI of protein

Is this correct  

Thank You  

[Winga]

Remind you one thing, the stability of a protein at certain pH range.

[jena]

The pH is stable at anything above 2(right) , if I looking the answer in relation to pH> pI, so the answer would be

b. pH=6

Thank You

[Winga]

The pH is stable at anything above 2(right) , if I looking the answer in relation to pH> pI, so the answer would be

b. pH=6

Thank You

I am not sure exactly the pH range, usually around 5 ~ 8 (referring to my notes), I think it is talking about the most stability.
If pH>pI, then we use anion exchange instead.

[Yggdrasil]

I am not sure exactly the pH range, usually around 5 ~ 8 (referring to my notes), I think it is talking about the most stability.

The pH range varies for a protein.  For example, proteases found in stomach juices are probably stable a very low pH values.  However, in general, you will want to be about 2 pH units from the pI of the protein when doing ion exchange.