Protocol for precipitation of proteins using ammonium sulphate

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Place an appropriate volume of the ammonium sulphate precipitate suspension into a centrifugation tube.
Collect precipitate by centrifugation at 5000 g or higher for 10 min at 4°C.
Remove supernatant fraction carefully, try to take out every last drop of ammonium sulphate solution.
Re-suspend pellet in a small volume of appropriate buffer and dialyse it against some 100-200 volumes of buffer. Make 2-3 changes, the last one should be left overnight for full equilibration. After 2 changes you can expect there to be about 1-2mM of ammonium sulphate left in the sample, with 3 changes it is close to 0.
It is useful to clarify sample from possible insoluble contaminants by centrifugation at 25000g or higher for 15 min.

NB: Remember that some proteins can not be recovered from ammonium sulphate precipitate.

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