loss of activity during as-precipitation

Peter Alliger u7q11aa at sunmail.lrz-muenchen.de
Fri Feb 10 08:49:20 EST 1995

I am using ammoniumsulfate precipitation to purity a transcription
factor but I only get about 30% of the input DNA-binding activity. 
I would like to keep this purification step as it helps me to 1)
concentrate the eluate from a Q-sepharose and 2) reduces the
KCl-concentration so I can use it directly for DNA-affinity

Does anyone have an idea how to improve the activity with this kind of
precipitation or is there any other purification step with the same

My protocol is the following:
-ad dropwise 4M AS while stirring on ice
-incubation for 30 min on ice
-centrifugation at 12000 rpm (sorvall)
-resolving the pellet in 1/5 vol
-dialysing for 2h at 4C

thanks for comments

Peter Alliger, Ph.D.                   
Institute for Immunology                
University of Munich                    

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