Immunoprecipitation is a method used for protein detection in a sample where proteins are expressed at low levels, have been post-translationally modified, or form parts of larger complexes or interactions.

Antibodies specific to the protein of interest are used to remove (precipitate) that protein from solution by adding the antibody and then adding a molecule complementary to the antibody that is insoluble, before spinning the solution to precipitate the antibody-protein complex and eluting it with SDS.

When detecting post-translational modifications of a protein, the insoluble antibody-binding protein used should be an anti-GATA-1. Then immunoprecipiated proteins should then be run on a gel, transferred to a membrane by Western blotting, and probed with an antibody against modified (acetylated) GATA-1.

Co-immunoprecipitation is the method used to identify proteins in complexes. An organelle (e.g. the nucleus) is first isolated by centrifugation and then an antibody is added that is specific to one of the proteins in the complex of interest. Then insoluble antibody-binding beads are added, and the immunoprecipitated proteins are washed and collected. Finally, a Western blot analysis is performed but this time using antibodies specific to the second protein in the complex of interest; if the two proteins interact then immunoprecipitation of one should enable the detection of the other. A 'pre-clearing' step should be performed to remove non-specifically bound protein; Marvel is often used to prevent non-specific protein binding.