Rabbit Anti-GST Tag monoclonal antibody for FC, ICC, IF, WB. GST (Glutathione S-transferase) is a 26kDa protein, present in eukaryotes and in prokaryotes, where they catalyze a variety of reactions. Glutathione Stransferase is used to create the GST gene fusion system. This GST-fusion protein can then be purified from cells via its high affinity for glutathione. Fusion Proteins offer an important biological assay for direct protein-to-protein interactions. The GST gene fusion system has been introduced into numerous expression vectors.