Ammonium sulfate saturated solution

Protein solubility is dependent on the ionic strength of the solution, among other factors. Two distinct phenomenon of protein solubilization are seen in general: 1) Salting in: At low salt concentrations, the solubility of the protein increases with increasing salt concentration (i.e. increasing ionic strength). 2) Salting out: As the salt concentration (ionic strength) increases, the solubility of the protein begins to decrease. At certain ionic strength, the protein will be almost completely precipitate from the solution. Since proteins differ markedly in their solubility at high ionic strength, salting-out is a very useful procedure to assist in the purification of a given protein. Ammonium sulfate has been widely used in salting out for protein purification, as it is very water soluble, forms two ions high in the Hofmeister series1, and has no adverse effects upon enzyme activity. It is generally used as a saturated aqueous solution which is diluted to the required concentration and expressed as a percentage concentration of the saturated solution (a 100% solution). While ammonium sulfate fractionation is a low resolution technique, it is used successfully to reduce the complexity and decrease the sample volume on a daily basis by many scientists.