ammonium sulfate precipitation of proteins

[Cornelius Krasel]

bipin dalmia (dalmiabk at phibred.com) wrote:
> i had 60 ml of 3 mg/ml protein solution, in 50 mM tris-hcl, 1 mM EDTA, pH
> 8.6. 
> i wanted to concentrate it before size exclusion chromatography so i
> decided to do a 85% ammonium sulfate precipitation. i added 36.6 grams of
> salt (slowly) to the 60 mL at room temp. and let it stir for 30 minutes
> after adding the last bit of salt. i saw the solution go all cloudy. then
> centrifugation at 20,000 g for 20 minutes and NO PELLET!!! can someone
> explain what happened

At high concentrations of ammonium sulfate the density of the solution can
get higher than the one of your precipitated protein; so the protein floats
around during centrifugation.

> and how i can recover my protein?

No idea :-(

--Cornelius.

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/* Cornelius Krasel, Abt. Lohse, Genzentrum, D-82152 Martinsried, Germany */
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