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best way to adjust pH of protein solutions?

Jim Owens jow at helix.nih.gov
Mon Jul 18 13:18:06 EST 1994

In article <305vv0$754 at news.iastate.edu> Bipin K Dalmia,
bipin at iastate.edu writes:
>what is the best way (quickest) to adjust the pH of a protein solution?
>dialysis takes too long and desalting/buffer exchange columns are out
>'cause i have 100 mL of solution and it would take a 10-story high
>column. directly adding acid/base would cause extreme local pH values
>and denature the protein. 
>i have to do this prior to running an ion-exchange column so i can't
>increase the ionic-strength too much either.

First, the disclaimer:  I never was much of a protein chemist, and it has
been 20 years since I even pretended to know what I was doing with them. 
I highly recommend checking with someone really knowledgeable before
taking any of _my_ suggestions.

1) Dialysis need not take very long.  Pencil-wide dialysis tubing which
is stirred along with the exterior buffer would be 95% equilibrated in
half an hour.  Granted 100ml would require a lot of this thin tubing. 
But 3 inch tubing for 60-90 minutes might work OK as long as the bag and
its contents are stirred vigorously.

2) Acetone precipitation followed by dissolving in the buffer of choice
should work as long as the protein can be easily redissolve.

3) Ammonium sulfate precipitation, with the same caveat.

4) TCA precipitation, same caveat.

5) You could dilute your 100ml into a liter or two of what you want for
the ion exchange chromatography and then run the ion exchange.  Ion
exchange chromatography can concencentrate the protein as long as you do
not exceed the capacity of the resin.

Those are my ideas for what they are worth.  (Every penny you paid.)  A
real protein chemist might want to know more details about the properties
of your protein before making suggestions, but I am a fool.  Perhaps you
should call technical support (for industrial applications) of Pharmacia.

Good luck,

Jim Owens

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