Precipitation with TCA and Na deoxycholate - what is the role of deoxycholate? (Oct/25/2004 )

I'm working on extracellular proteins of bacterium, by bidimensionnal electrophoresis.
To recover these proteins, I precipitate the culture medium filtered, with TCA. I saw that in certain protocols, deoxycholate was added before precipitation. I tested this protocol and deoxycholate enabled me to recover a greater quantity of proteins. However, I don't know the role of sodium deoxycholate. Can you tell me what is its role?

Thank you very much.

I personaly use deoxycholate in lysis buffer to release membrane proteins... it is a mild detergent...

Simon

deoxycholate binds to the protein and increases the interaction with the TCA. You usually add it for precipitation of very small amounts of protein with TCA..

Thank you for your answer!

Deoxycholic acid is added in base form (sodium salt) and precipitates after addition of the stronger acid TCA. In this protocol, it acts as a coprecipitant and helps the protein to precipitate. Yes, it also is a detergent and binds to the protein in solution through hydrophobic interactions of its cholesterol-like hydrocarbon structure with hydrophobic parts of the proteins. Since one wants it to bind to the proteins before precipitation, you need to add it to the proteins before adding TCA.