We routinely use a P200 to pipette drops of protein directly into a small Dewar of liquid nitrogen. The protein forms small BB's with a volume of approximately 30 micro-L each. Pipette slowly, allowing the drops to freeze solid before adding the next one. The frozen BB's can be picked up with forceps or a slotted spoon and stored in a cryovial in the -80 freezer. For future experiments, you can thaw only what you need. I have only seen one protein that couldn't recover from this and could only be crystallized prior to freezing.
A systematic study of this procedure is described in Deng et al. http://www.ncbi.nlm.nih.gov/pubmed/14684931 --Andrew On 11/5/10 3:40 PM, "<Eric Karg>" <harvard...@yahoo.com> wrote: Dear all, I'm working on a protein which starts to precipitate after 3-4 days of storage at 4 degrees or room temperature. The storage buffer contains 300 mM NaCl because at lower salt concentrations it also tends to precipitate. Different buffers and adding glycerol did not help although this was not done in a systematic way. Has anyone had similar experiences? Any suggestions to overcome this problem? Thanks in advance! Eric -- Andrew M. Gulick, Ph.D. ----------------------------------- (716) 898-8619 Hauptman-Woodward Institute 700 Ellicott St Buffalo, NY 14203 ----------------------------------- Hauptman-Woodward Institute Dept. of Structural Biology, SUNY at Buffalo http://www.hwi.buffalo.edu/Faculty/Gulick/Gulick.html http://labs.hwi.buffalo.edu/gulick