Immunoblotting: Preparing Immunoprecipitated Proteins Protocol Protein immunoprecipitation can be a useful preparative step for immunoblotting. For very rare proteins, the protein of interest can be purified and concentrated by standard immunoprecipitation techniques before immunoblotting. In addition, protein-protein interactions can be tested with an immunoprecipitating antibody that is specific for one protein of a complex and an immunoblotting antibody that is specific for a second member of the complex.
Western Blot Analysis of Endogenous Gene Expression Protocol Procedure describes how it denatures most of the modification and degradation proteins immediately giving the most accurate read out of the true levels of protein at the time of harvest. However, in cases where detection is a problem, a limited purification (e.g. isolation of nuclear extract for the detection of transcription factors) might be required to allow analysis.