I think it is not so much about gentleness of "solid to gas" over "liquid to
gas" than what happens in aqueous condition. At temperatures where water is
liquid, most enzymes/proteins are more prone to degradation than they are at
sub-zero temperatures used for "freeze drying", viz -20 to -40 C. Also, most
enzymes are inactive or minimally active in solid phase at sub-zero temps, thus
minimizing enzymatic degradation of proteins. Hence, if you have a large volume
of sample you are better off freeze drying, where the sample is not allowed to
go above -20 (usually) and the water is directly sublimated. For a tiny sample
of say 100uL, a speed vac with the chamber cooled may work just fine since
often the sample in the speed vac freezes (especially if in very low salt
buffer, and since the g is not very high) during evaporation and also because
the time to dry is "short". Finally, the choice really depends on the type of
protein and its lability under different conditions.
Quoting Greg Pankhurst <g.pankhurst at cfi.unsw.edu.au>:
> Hey All
>> Just wanted to canvas opinions on the advantages of using a Freeze Dryer
> to dry proteins down over using a Speed Vac.
>> My understanding was that the solid -> gas transition was gentler than
> the liquid -> gas transition, and thus you were far less likely to see
> things like oxidation occuring with a freeze dryer. Is this about right
> or am I miles away ??
>> Thanx in Advance
> Greg Pankhurst
>
--
Hiranya S. Roychowdhury, Ph.D.
Coll. Asst. Professor,
Molecular Biology,
Dept. of Chemistry & Biochemistry
Rm# 336, Chemistry Bldg.; MSC 3MLS
New Mexico State University
Las Cruces, NM 88003
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