Ammonium Sulfate Precipitation

Ammonium Sulfate Precipitation (NH₄)₂SO₄ is a method of protein purification by solubility. When proteins are in an aqueous solution a sphere of hydration is formed around each molecule. This sphere inhibits the protein to interact with other proteins. When an Ammonium Sulfate Precipitate is added, it dehydrates the solution and the protein precipitates out. The assay activity will be determined by the protein's tendency to precipitate (i.e. the amount of Ammonium Sulfate that needs to be added to the solution for the protein to precipitate). This method is also referred to as Salting-Out.