Hi, if it is Tris buffer , then your ph should be near neutral as it best maintains the GST function. 7.5 to 7.6. The following can work well: lysis buffer containing 50 mM Tris•HCl, pH 7.4, 150 mM NaCl, 1 mM EDTA, 1% Nonidet P-40, 5 mM Na3VO4, 20 mM NaF, 10 mM sodium pyrophosphate. 

Thanks, Emmanuel, actually I have a protocol working well, and just a friend come to ask me a question of the pH which I didnot pay attention to before. I did a bit literature research and it seems the neutral pH is actually not the best for the solubility and then I am wondering why many protocols (including mine) choose this pH range. Want to know a bit more detailed fundamental mechanism on it. But thanks anyway. Cheers, Bin

This pH is used because it is similar to the cytoplasmic pH of eukaryotic cells, and therefore a pH at which the extracted proteins are likely to be stable.

Thanks Adam, and should this pH be determined by solubility of the proteome as well? or the other reagents in the buffer like detergent would more likely contribute to dissolve the proteins? My concern is I am not sure if the selected pH will be the optimum in terms of solubility, or maybe it is a balance between stability and solubility?

The non-membrane proteins in the cytoplasm are already soluble, so extracting them in a buffer of about the same pH, which also dilutes them, will result in these proteins being soluble in the extract. Integral membrane proteins are not soluble unless the membrane is dissolved by the use of detergent. Peripheral membrane proteins may be extracted, in some cases, by chaotropic agents such as sodium carbonate or sodium bromide, or by the use of detergents. Proteins that are soluble in acidic compartments (lysosomes and endosomes) may not be soluble at neutral pH when concentrated, but probably will be soluble in a dilute form in an extract. You should also think about the need for a reducing agent. Since cytoplasmic proteins are in a reducing environment, the extraction buffer should contain a reducing agent to prevent disulfide oxidation. You should also include a protease inhibitor cocktail in the extraction buffer.

I think many people are unduly concerned about the isoelectric point of proteins. A protein at its isoelectric point has zero net charge, but that does not necessarily make it insoluble. This can be an issue sometimes for concentrated, purified proteins, but I don't think it is an issue for proteins in a cell extract.

Thanks, Adam, very helpful answers.

Dear Bin Lai and all the above scientist:-

If possible to see the following link

https://www.sciencedirect.com/topics/neuroscience/lysis-buffer

Hope to be helpful...Regard

Thanks, Kou. Will have a look at the papers.

Thanks, Mushtak, useful collections.