MadSci Network: Biochemistry

Re: How does these precipitating agents works?

Date: Sat Feb 28 22:36:38 2009
Posted By: Karin Crowhurst, Assistant Professor, Biochemistry
Area of science: Biochemistry
ID: 1235854150.Bc

Hi there,

For things like salts, particularly ammonium sulfate (which is very popular to use), increased concentrations of these salts in solution will interact with the charged side chains on the protein surface and therefore interfere with the interactions those charged side chains were having with water. This consequently increases the preference for protein-protein interactions, causing aggregation and therefore precipitation. It's also known as "Salting out".

I found a paper that might be useful to you in your efforts to figure out how ethanol works: it even talks with respect to serum albumin.

Addition of acids will lower the pH of the solution. If you lower it enough then the protein will denature, then aggregate (due to increased hydrophobic interactions) and then crash out of solution.

Hope this helps,


C. J. van Oss (1989)
On the mechanism of the cold ethanol precipitation method of plasma protein fractionation
Journal of Protein Chemistry 8 (5):661-668.

[Moderator's Note: Neil Saunders has written an excellent answer about salting out that you should also read. -- Steve Mack]

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