Recombinant protein precipitating upon freezing

[Kyle Legate]

marguerite.b.colas from gsk.com wrote:
> Hello Peter!
> 
> I work at a pharmaceutical company and have been working on this study 
> that involves freezing hemoglobin proteins, Every time we thaw our samples 
> we notice that they go cloudy.
> At first we thought that we had been mixing our cell membrane pellet with 
> the cell content supernatant. However, the time we took extra care to 
> distinguish the supernatant from the pellet, we still noticed that our 
> samples went cloudy after thawing them from the freezer. All our samples 
> are kept in a -20c freezer.
> 

Is there a reason you're keeping them at -20C? Normal protein storage is 
at -80C, unless you're working with an enzyme that loses activity upon 
freezing, in which case -20C in 50% glycerol is acceptable. You can try 
adding glycerol to 50% to keep the protein cold but not frozen.