Am 08.03.2008, 17:01 Uhr, schrieb Tsu-Fan Cheng <tfcheng from gmail.com>:
> The idea of AS ppt is to remove residual PEI from the solution.
> However, this time the PEI is still there and my protein precipitated.
Almost any protein can be precipitated with AS, that is just a question of
concentration. Some proteins already precipitate at 20% satturation,
others only at 80%.
In this case you apparently have a protein that precipitates at relatively
low conc of AS, before the PEI precipitates. That's fine, just spin down
the protein, remove the supernatant with the PEI, wash the precipitate
with AS solution of the same conc as used for pelleting, spin again,
discard the supernatant and redissolve your protein in a buffer of your
choice.
Depending on what you want to do you may have to remove the remaining AS
by either dialysis or gel filtration (''desalting column'').
Note also:
- many proteins store very well as AS precipitate in mother liquor at 4
deg C.
- Add the AS slowly and in the cold. Stop the addition when just a slight
haze develops in the protein solution, than keep o/n in the fridge. That
way you get best separation between your protein and whatever remains in
solution.
- Any book on protein purification will discuss this in more detail.
