We plan to send proteoliposomes to a cooperating group and are wondering whether it is ok to send them on dry ice (after flash freezing in liquid nitrogen). This would be a lot cheaper than sending them in a dewar. It doesn't matter too much if the proteolipomes become more leaky as they won't be used for transport assays, but we do want to look at the effect of the lipid bilayer on the incorporated membrane protein. I wonder if anyone has experience with sending proteoliposomes on dry ice, if so please tell me if they were still usable afterwards. Thanks!
Provided they were flash frozen originally in liquid nitrogen, then I am sure the protein will be fine when the proteoliposomes are sent in dry ice. The retention of transport activity depends very much on how the thawing is carried out; rapid thaw is good for some types of transporter, and slow thaw for others in our experience.
In my experience proteoliposomes could not be stored in dry ice. However, it depends on the incorportated protein. Therefore, the best is checking before if after freezing and thawing the protein activity/properties remain the same.
Cesare
I worked with proteoliposomes that I received on dry ice and they were fine.
It's very reasonable to send proteoliposomes on dry ice. One thing to keep in mind, though, is that freezing tends to favor forming multilamellar vesicles--we often include ~200 mM sucrose to try to prevent this from happening. But certainly check your protein thawed at home to make sure it behaves well.
We do this routinely with LacY. The sample does get a little more turbid, but our collaborators sonicate it a few times and everything is fine.
In my experience most proteins are fine frozen once they are reconstituted in proteoliposomes. This might not be true for all of them and might depend on the efficiency of reconstitution.
Dear Josy, I agree with Cesare. Simply check before you send them to your collaborator. Easy experiment to do (well relatively speaking).
Edgar
I always isolate vesicles from different organs, as I work on some of the membrane transporters. In my experience, the activity of some membrane proteins can be negatively affected as a result of freeze-thaw fractionation (cycles) ( although this would differ from one protein to another, and how many cycles). However, it would be better if you can measure enzyme activity for one or two of the enzyme marker such as alkaline phosphtase or leucine aminopeptidase. and compare before/after. For most of the membrane proteins that I have dealt with, there had not been any changes in the protein activity after the transfer from - 80 to 24 hour in -4 fridge
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