Direct immunoprecipitation of protein

Many biochemical experiments depend on the measurement of the amount of an enzyme (or other protein) independently of any enzymatic activity it may have. When working with cell-free extracts or other complex mixtures this is not simple to do, and most procedures that have general application involve the use of antibodies. Two distinct strategies have been used to good effect. The amount of antibody bound can be made to reflect amount of antigen, as in an ELISA assay (ref. 1 and Vol. 1 of this series) or in a "Western blot" (ref. 2 and Chapters 28 and 29 in this volume). Alternatively, the antibody can be used effectively to purify the antigen protein. The method described here is of the latter sort and has advantages of simplicity and rapidity both over ELISA and blotting techniques, on the one hand, and indirect precipitation techniques on the other.