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Specialty Chemistry Forums => Biochemistry and Chemical Biology Forum => Topic started by: jena on September 26, 2005, 08:55:57 PM

Title: Cation exchange question
Post by: jena on September 26, 2005, 08:55:57 PM

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  :)

Title: Re:Cation exchange question
Post by: Winga on September 27, 2005, 08:28:47 AM

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

Title: Re:Cation exchange question
Post by: jena on September 27, 2005, 01:55:21 PM

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 :)

Title: Re:Cation exchange question
Post by: Winga on September 27, 2005, 02:35:26 PM

Quote from: jena on September 27, 2005, 01:55:21 PM

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.

Title: Re:Cation exchange question
Post by: Yggdrasil on September 27, 2005, 02:54:05 PM

Quote from: Winga on September 27, 2005, 02:35:26 PM

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.