... without an aggressive elution. Also immunoaffinity assays can be very sensitive since they rely on antibodies recognising and binding to the proteins that you are trying to detect but it is difficult to elute those proteins because they are held so tightly. The first method of purification that I shall describe is also one of the simplest. It relies on the physical properties of the protein itself by making the desired protein precipitate out whilst keeping other proteins and 'background' matter in solution. Protein solubility can change as ionic strength of the solution changes and generally they have different solubility curves, but a general trend is that protein solubility decreases as ionic strength of the solution increases. So if you have a mixture of proteins then carefully increasing the salt content can precipitate out some proteins but not others if they react in different ways to the change in ...

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