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Ammonium sulfate precipitation is a useful technique as an initial step in protein purification because it enables quick, bulk precipitation of cellular proteins. [4] It is also often employed during the later stages of purification to concentrate protein from dilute solution following procedures such as gel filtration .
Salting out (also known as salt-induced precipitation, salt fractionation, anti-solvent crystallization, precipitation crystallization, or drowning out) [1] is a purification technique that utilizes the reduced solubility of certain molecules in a solution of very high ionic strength.
By contrast, later salts in the series increase the solubility of nonpolar molecules ("salting in") and decrease the order in water; in effect, they weaken the hydrophobic effect. [ 14 ] [ 15 ] The "salting out" effect is commonly exploited in protein purification through the use of ammonium sulfate precipitation . [ 16 ]
The most commonly used salt is ammonium sulfate. There is a low variation in salting out over temperatures 0 °C to 30 °C. Protein precipitates left in the salt solution can remain stable for years-protected from proteolysis and bacterial contamination by the high salt concentrations.
The following chart shows the solubility of various ionic compounds in water at 1 atm pressure and room temperature (approx. 25 °C, 298.15 K). "Soluble" means the ionic compound doesn't precipitate, while "slightly soluble" and "insoluble" mean that a solid will precipitate; "slightly soluble" compounds like calcium sulfate may require heat to precipitate.
Ammonium sulfate precipitation is a common method for protein purification by precipitation. As the ionic strength of a solution increases, the solubility of proteins in that solution decreases. Being extremely soluble in water, ammonium sulfate can "salt out" (precipitate) proteins from aqueous solutions.
Proteins of the erythrocyte membrane separated by SDS-PAGE according to their molecular masses. SDS-PAGE (sodium dodecyl sulfate–polyacrylamide gel electrophoresis) is a discontinuous electrophoretic system developed by Ulrich K. Laemmli which is commonly used as a method to separate proteins with molecular masses between 5 and 250 kDa.
Ammonium chloride precipitates and is removed by filtration, and the solution is recycled to produce more sodium carbonate. Hou's process eliminates the production of calcium chloride. The byproduct ammonium chloride can be refined, used as a fertilizer and may have greater commercial value than CaCl 2, thus reducing the extent of waste beds.