Protein samples still in liquid form at -20C - Storage condition for proteins (Sep/17/2005 )
Dear folks,
Please help me out. I store my purified protein samples at -20C and they are still at the liquid form (a few are frozen) at this temperature! 
I used Trizol kit to purify them and dissolved them in a solution of 9M urea, 4% CHAPS and 30mM Tris/HCl pH 8.5 buffer. They had very high concentrations to start with, but with time the concentrations are less than before. Can their liquid form degrade them? How can i store my protein samples better? At -70C? I have asked some people and they store theirs at -70C.
Thank you all for your kind help!
Please help me out. I store my purified protein samples at -20C and they are still at the liquid form (a few are frozen) at this temperature!
I used Trizol kit to purify them and dissolved them in a solution of 9M urea, 4% CHAPS and 30mM Tris/HCl pH 8.5 buffer. They had very high concentrations to start with, but with time the concentrations are less than before. Can their liquid form degrade them? How can i store my protein samples better? At -70C? I have asked some people and they store theirs at -70C. Thank you all for your kind help!
I always store my protein samples at -80 degrees.
But if your samples do not freeze at -20, it suggests that they contain a huge amount of salt.
Thanks, Theo.
Do you think that this liquid form could degrade my proteins? How about the phenol ethanol supernatants of the proteins. Do you also store them at -80C?
Do you think that this liquid form could degrade my proteins? How about the phenol ethanol supernatants of the proteins. Do you also store them at -80C?
If your proteins are enzymes that still should contain enzymatic activity, this activity most probably will get lost if you keep the proteins in too high salt concentrations (this differs for each protein).
I'm not sure what you mean with phenol ethanol supernatants of the proteins. I only use phenol to clean my nucleic acids.
I do not use my proteins to test for their enzymatic activity. I need them for western blot. Can you figure out why the concentrations are less than before?
I think the protein concentrations may be going down due to proteolytic activity of proteases. (please correct me if I am wrong)
I have noticed that even if I added a good amount of Na vanadate, PMSF and other protease inhibitors...my protein concentrate from cell lysates still becomes less. Therefore, as a rule I onnly make up the protein lysates for westerns just before running the gel. I just freeze my cell pellet. Also I never reuse my protein lysates.
Good luck
p..
PS: The makeover for the page is good...whoever it is.. keep up the good work.
How do you measure protein concentration? Because even if you would have proteolytic degradation, the aminoacids are still present in your sample. So it will depend on the method you use what the result would be.
. Can you figure out why the concentrations are less than before?
How do you measure protein concentration? Because even if you would have proteolytic degradation, the aminoacids are still present in your sample. So it will depend on the method you use what the result would be.
I use Bradford method.
My best advice would be to freeze in liquid N2 and transfer to -70ºC...