concentration of low molecular weight protein

Peter pxpst2 at
Fri Sep 19 09:09:10 EST 1997

In article <34221F3A.6F29 at>, leakeya at wrote:

.> How do I concentrate a low molecular weight protein (less than 5kDa)
.> from gel filtration fractions ie. dilute???, keeping in mind that
.> filtration devices and dialysis tubing concentrate above this size.
.> I have tried ammonium sulphate precipitation (up to 80%) with poor
.> results. It just doesn't want to precipitate!!!

Why precipitate your protein.  Precipitation of protein has three big
problems and you have run into two of them.
the thre problems are 1) does not work well with dilute proteins
                      2) does not work well with small proteins
                      3) proteins often hard to resolvate

the solution to your problem is to do a phase extraction with Phenol.

A good paper for reference is "Concentration of Dilute Protein for
Electrophoresis", Anal. Biochem., 226, 382-383 (1995).

Hope this helps, BTW I had the same problem and it really slowed my work.


"Don't you eat that yellow snow
watch out where the huskys go"

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