Protein concentration with PEG
Dr Engelbert Buxbaum
(by engelbert_buxbaum from hotmail.com)
Sat May 19 11:23:07 EST 2012
In article <jnphnv$npj$2 from news.albasani.net>, dk from noemail.thankstospam.net
> >You are probably aware of the protein concentration method by
> >"dialyzing" against polyethyleneglycol.
> >We just got some concerns now that some of the PEG could make it
> >across the membrane.
> I'd advise you against using PEG. All PEGs are "dirty" and you will inevitably
> get something into your protein. The same idea but much cleaner is to use
> dried polyacrylamide gel that swells a lot. That's what we do with proteins
> that cannot be concentrated by standard ultrafiltration. Buy this and be
This of course has the disadvantage to cost some $20 per 5 ml sample.
There are two things to consider here: low molecular PEG that can cross
the membrane and other contaminants. The former are probably relatively
benign, especially when further purification steps follow. PEG actually
stabilizes protein conformation, that is why it is used in protein
Other contaminants are a different story, in particular peroxides. It
might be worthwhile to test each batch for those and to keep the PEG
dark, cool and dry.
That said, I have used the procedure many times, and never had any
problems. However, that was with 20 kDa PEG and a 6 kDa membrane rather
than 14 kDa as described by the OP.
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