Re: How does these precipitating agents works?

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: http://www.springerlink.com/content/gm71273l642708h3/ 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,

Karin

Reference:
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.
10.1007/BF01025606

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