John Marcus J.Marcus at
Tue Jan 10 22:24:21 EST 1995

In article <3euc3i$3ib at>, u7q11aa at (Peter Alliger) says:
>I am looking for good method to precipitate a highly purified protein
>analysing it on a SDS-PAGE.
>The fraction has about 1M KCl and should be concentrated from 500 ul to
>about 20.
>Thanks for suggestions
Have you thought about using a Centricon or Microcon centrifugal
filtration device.  Essentially, you put your protein sample into
the microcon (~500ul capacity) and then spin in a microcentrifuge
for 1 min to 30 min (depending on the molecular weight cutoff of 
the filter that you are using at the time).  I think Amicon may 
have molecular weight cuttoffs as low as 1000Da.  When you are done 
spinning you should be left with about 10ul volume if you use a
microcon; although, this holdup volume is not very predictable.  

Alternatively, you could desalt your sample with the microcon; 
recover it and then proceed to dry your sample with a stream of 
nitrogen or else a speedi-vac hooked up to a vacuum pump.

I hope that is helpful.

John Marcus

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