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Western Blot antibody
I would recommend using protein A beads, as protein A has a higher affinity for rabbit immunoglobulins compared to protein G.
It appears that the secondary antibody has bound to the reduced rabbit IgG that was used in the IP, which appears as bands around 25 kDa (light chain) and 50 kDa (heavy chain). Although the secondary antibody would be anti-mouse, secondaries do often cross-react with IgG from similar species unless they are pre-adsorbed to ensure no cross-reactivity.
To reduce this background, you can use a secondary antibody that will only bind to non-reduced IgG following the Western blot with ab26246, such as ab131368.
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Submitted Jul 11 2012