The western blot (sometimes called the protein immunoblot) is a widely used analytical technique used to detect specific proteins in a sample of tissue homogenate or extract.
Western- or immunoblotting is a commonly employed technique for the detection of protein antigens in complex mixtures. Samples are first separated by SDS-polyacrylamide gel electrophoresis. The separated proteins are then transferred to a membrane (usually nitrocellulose, polyvinyl pyrolidon, or nylon). These membranes are incubated with an antibody specific for the protein of interest which binds to the protein band immobilized on the membrane. The antibody is then visualized with a detection system that is usually based on a secondary protein binding to Ig chains which is linked to a color-yielding reaction.
There are many reagent companies that specialize in providing antibodies (both monoclonal and polyclonal antibodies) against tens of thousands of different proteins. Commercial antibodies can be expensive, although the unbound antibody can be reused between experiments. This method is used in the fields of molecular biology, immunogenetics and other molecular biology disciplines.
It is not uncommon that, contrary to the theoretical predictions, several bands are detected. Although it is possible that an antibody is not entirely specific for the protein, other factors may be responsible.