We are using different protocols for different proteins. But our aim is to analyze the protein by LC-MS/MS under ISO 17025 norm... We did not found an "universl" precipitation procedure.

Try formic acid, perchloric acid, acetic acid or tertiobutyl-methyl-ester. Start at 2% for the acids and with a slow "titration" of ester.

It's long, but you should be able to obtain procedure fit for your purpose.

We have had very good experience using the Calbiochem ProteoExtract Protein Precipitation Kit.

Precipitation is very efficient and pellets are relatively easy to redissolve. only downside is that it is more expensive than standard protocols.

Alternatively, try Wessel-Flügge Protocol (http://www.ncbi.nlm.nih.gov/pubmed/6731838, or http://www.biologie.uni-konstanz.de/fritz/documents/Protein_precipitation-methods.htm)

Good luck!

I usually try to keep my proteins as soluble as possible especially before IEF. I have found some proteins particularly difficult to resolubilize for gel analysis . However for final purity proteins i sometimes use an ice cold acetone method 1 part protein solution 19 parts acetone usually overnight at -20 C.

Like Stefan, I would also recommend the chloroform-methanol precipitation method by Wessel-Flügge. However, it is less applicable to larger sample volumes.

Thanks to everyone for the valuable answers. I searched some about the chloroform-methanol method, but as Kasper mentioned above it is not applicable for large sample volumes. And in my case I do have a pretty large volume starting with. Maybe I will try to use the calbiochem precipitation kit.

When doing TCA precipitation, re-solubilization of the resulting pellet is often easier when adding 10% glycerol in sample prior to precipitation. If you have enough sample to play with, maybe this is something to test out...