[Protein-analysis] PEI and ammonium sulfate ppt

Tsu-Fan Cheng via proteins%40net.bio.net (by tfcheng from gmail.com)
Sat Mar 8 16:01:28 EST 2008

I am purifying a protein with a protocol that I used last time to
purify a similar protein. This protocol involves PEI
(polyethyleneimine) fractionation and ammonium sulfate precipitation.
The idea of AS ppt is to remove residual PEI from the solution.
However, this time the PEI is still there and my protein precipitated.
The only difference I can tell from this exp to the last one is that I
dissolve the AS ppt pellete with a solution containing 250mM NaCl,
which is none in the previous exp. I thought the [NaCl] won't matter
since PEI should be removed after AS ppt. I wonder if someone can
explain PEI+AS procedure to me so I have a better understanding and
control over this protocol in the future. thank you.

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