
a few questions about ion exchange chromatography
#16
Posted 28 November 2011 - 12:26 PM
talent does what it can
genius does what it must
i used to do what i got paid to do
#17
Posted 29 November 2011 - 12:54 AM
I want to ask you something again.
pH of my protein solution is about 8.20. However, I equilibrate the column with pH=7.4. Should I pour my protein solution to the equilibration buffer in order to obtain the pH of protein solution near 7.4?
What must be done when pH of a protein solution is above or under the pH of equilibration buffer? (I use equilibration buffer when i wash the column after flowthrough) If I do this, can protein precipitate?
For example, I want to use cation exchange chromatography. pI of my protein is 7 and pH of my protein solution is 7.50. What should be done?
OR should I add HCl or NaOH to the protein solution to bring to near the pH of equilibration buffer?
Edited by xaxax, 29 November 2011 - 01:31 AM.
#18
Posted 29 November 2011 - 09:13 AM
are you using the same protein as before? before you said that the pI is 8.21 now you say 7. if you want to switch to cation exchange then the pH has to be lower than the pI.
talent does what it can
genius does what it must
i used to do what i got paid to do
#19
Posted 29 November 2011 - 01:21 PM
Edited by xaxax, 29 November 2011 - 10:24 PM.
#20
Posted 01 December 2011 - 09:00 AM
yes. keep in mind that you will be increasing the ionic strength of the solution. this may affect binding to the matrix.Do you suggest me to add buffering salt like Na2HPO4 or NaH2PO4? OR both of them?
you can dialyze against the equilibration buffer to adjust the ionic strength.
talent does what it can
genius does what it must
i used to do what i got paid to do
#21
Posted 07 December 2011 - 10:41 AM
How can I regenerate my column?
I found 3 methods. Which of them is convenient for my column? and for regenerating columns?
1) wash column with 4 bed volumes 0.5-1M NaOH, then with 2-3 bed volumes pf water
wash with 4 bed volumes of 70% ethanol followed by 4 bed volumes of water
wash with 2 bed volumes of 0.5-1M HCl and 4 bed volumes of water
wash with starting buffer to equilibrate
2) wash column with 70% ethanol then with water
wash with 0.5-1M HCl and with water (to neutralize)
wash with 0.5-1M NaOH and with water (to neutralize)
wash with starting buffer to equilibrate
3) wash with 70%ethanol
if it is a cation column,wash with 0.5-1M HCl and water
wash with starting buffer to equilibrate
or if it is an anion column, wash with 0.5-1M NaOH and water
wash with starting buffer to equilibrate
#22
Posted 08 December 2011 - 12:52 PM
i only regenerate when capacity significantly diminishes. then i regenerate by cycling with acid and base (flushing with water in between), the order depending on whether it is anion or cation exchange.
never saw procedure using ethanol.
there is a method to clean the exchanger given in the handbook.
talent does what it can
genius does what it must
i used to do what i got paid to do
#23
Posted 11 December 2011 - 11:51 AM
since i use cation column, firstly, i should wash with acid (to remove the unwanted bounded proteins) and water (to neutralize). After that, I should wash with base and water. Then, I should equilibrate the column with starting buffer. ???
#24
Posted 12 December 2011 - 07:20 AM
the scheme you laid out to regenerate looks fine, just make sure that you don't exceed the recommended concentration of acid/base for your matrix. make sure you flush with a large volume of water between the acid and base treatments.
as i said before, high salt washes and re-equilibration are sufficient most of the time (until binding capacity has significantly diminished).
talent does what it can
genius does what it must
i used to do what i got paid to do
#25
Posted 26 December 2011 - 02:29 PM
I want to ask something, again. :-)
This time, i want to make gst purification, but I want to learn 3-4 important and basic question by means of your knowledge and experience.
1) What should the pH of protein solution to be loaded be?
2) What temperature should be used for gst purification? It is suggested both 4 C and room temperature. According to the temperature, the pH of equilibration and elution buffers will change.
3) Are there any elution buffers except for tris buffer?
4) Some articles suggest PBS for equilibration and washing the resin. And some suggests tris buffer for equilibration, wash and elution (with reduced glutathione).
#26
Posted 27 December 2011 - 10:03 PM
2) i always prefer to run at 4C but if run rapidly (e.g. if run on hplc or fplc) and the fractions are put on ice immediately then room temperature should be okay.
3) depends on the pH at which you run the column and the buffering range of the buffer. as you point out in your next question, phosphate buffers work fine.
4) use whichever suits your needs better.
you may want to download these 2 handbooks from gehealthcare life sciences:
gst gene fusion system
and
affinity chromatography
talent does what it can
genius does what it must
i used to do what i got paid to do
#27
Posted 02 January 2012 - 11:14 PM
Wash was made with 10 bed volumes twice. Elution was made with 2 bed volumes three times.
SDS page image was like that:
There was no loss of the desired protein with Flowthrough and Wash steps. However, in the elution step, the desired protein could not be seen. I thought that the protein might have been in the resin, then, I applied the elution buffer containing 20mM glutathione, however, I could not see the desired protein.
#28
Posted 04 January 2012 - 05:59 AM
is there more salt in the equilibration buffer than in the elution buffer?
routinely in ion exchange chromatography, elution buffers are equilibration buffer with higher salt concentrations. you may want to add salt to your elution buffer so that it is more concentrated than the equilibration buffer.
talent does what it can
genius does what it must
i used to do what i got paid to do
#29
Posted 09 January 2012 - 11:56 PM
My equilibration-wash buffer contains 4.3mM Na2HPO4, 1.47mM KH2PO4, 137mM NaCl, 2.7mM KCl.
and the elution buffer contains only 50mM Tris and 10mM glutathione (pH=8)
These buffers are suggested by the GST resin supplier.
I equilibrated the pH of the equilibration-wash buffer to the pH of the protein solution.
After I carried out ion exchange purification, I want to polish my protein with gst purification.
In my opinion, the equilibration-wash buffer and the elution content for the GST purification should be the same as the protein solution which is eluted from ion exchange. Content of the protein solution-taken from ion exchange- is 100mM NaCl, 5mM Na2HPO4, 1mM EDTA.
In addition to this, I think that the working pH should be same with the protein solution-taken from ion exchange- in every step of GST purification.
Edited by xaxax, 10 January 2012 - 01:45 AM.
#30
Posted 10 January 2012 - 09:32 AM
polishing is normally performed by gel filtration. affinity is a further purification step (and probably should have been done first).
talent does what it can
genius does what it must
i used to do what i got paid to do