Ian A. York iayork at
Thu Mar 15 14:30:46 EST 2001

In article <20010315191005.12388.qmail at>,
Manjili  <mmanjili at> wrote:
>buffer or PBS. I incubate antibody-antigen at 4 degree for 2 h and then add
>protein A sepharose to the mixture followed by incubation at 4 degree
>overnight while rotating.

Overnight is way longer than necessary, and can definitely cause
non-specific binding.  Try adding antibody for 1 hour on ice, and then
protein A-sepharose for 90 minutes while rotating.

Also consider the possibility that it's not actually binding, but proteins
coming out of solution (or not being cleared properly): if the protein
precipitates, then it'll come along with your protein A-sepharose pellet.  
Spin the lysate aggressively before adding antibody.  Or, if you don't
mind spending a bit of money, try Spin-X microfuge tubes or something
similar: a .45 micron filter clears the lysate out very nicely.

    Ian York   (iayork at  <>
    "-but as he was a York, I am rather inclined to suppose him a
     very respectable Man." -Jane Austen, The History of England

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