Anti-PA affinity gel is a chromatographic resin that contains immobilized anti-PA monoclonal antibodies. This gel is used to purify proteins that have been fused to the PA (protein A) peptide tag. The PA tag is a short amino acid sequence derived from the protein A of Staphylococcus aureus. How Anti-PA Affinity Gel Works: Protein binding: The PA-tagged protein binds specifically to the anti-PA antibodies immobilized on the gel. Washing: Unbound proteins are washed away. Elution: The bound PA-tagged protein is eluted from the gel using a competitive elution buffer that contains free PA peptide.