Protein A is the name of a protein found on certain bacterial cell walls. The protein has a binding site for Immunoglobulin G (IgG). This ability to bind IgG has been protein A a useful tool for research laboratories. Protein A has many uses. If conjugated to a detectable marker, such as a fluorescent marker or an enzyme, it can be used to detect antibodies. Protein A can also be used to purify total IgG from a solution. Also it can be used for immunoprecipitation as a way to purify a molecule of interest using a solid support system.