Using antibodies directed against a specific protein (antigen), we can identify the abuandance and molecular weight of a protein and whether it is present in the particular sample we are analyzing.

Antibodies can also be used to purify native proteins and their associated binding partners (i.e., protein complexes). Once bound to the antigen in an extract, the antibody-antigen complex is captured using protein A coupled to sepharaose beads. The purified proteins are then resolved by SDS-PAGE and visualized by Western blot or by autoradiography.

To determine the sub-cellular localization of proteins, cells are fixed, permeabilized and then incubated with an antibody against the protein of interest. A secondary antibody coupled to a fluorophore is used to detect the primary antibody as shown in the examples below.

Pulse-chase experiments label a sub-population of protein in the cell in order to track its sub-celluar transport. As diagrammed in the cartroon below, this technique can be used in conjunction with metabolic labeling procedures to "pulse" label newly synthesized proteins and "chase" labeled proteins to their final distination in the cell. Sub-cellular fractionation followed by immunoprecipitation, SDS-PAGE and autoradiography are used to locate the radioactive protein in the cytosic and nuclear fractions.