Immunoprecipitation, commonly referred to as IP, involves the binding of proteinaceous antigen in solution by an antigen-specific antibody followed by purification of the antigen-antibody complex via attachment to a solid-phase matrix such as Protein A or G agarose. This rather simplistic and rapid technique yields highly purified immune complexes from multifactorial solutions, including cell lysates or homogenized tissues, and is most commonly used to identify and determine the relative abundance of interacting proteins, referred to as coimmunoprecipitation or co-IP. Although methods encompassing immunoblotting or western blotting of cell lysate preparations can also be applied to determine the presence and quantity of a specific antigen, its relative molecular weight, rate of synthesis or degradation, and state of target-specific posttranslational modification, immunoprecipitation can significantly increase the sensitivity for these methodologies.
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