The glutathione S-transferase (GST) family of enzymes comprises a long list of cytosolic, mitochondrial, and microsomal proteins that are capable of multiple reactions with a multitude of substrates, both endogenous and xenobiotic. Mammalian cytosolic GSTs are dimeric both subunits being from the same class of GSTs. The monomers are in the range of 22C29 kDa. Glutathione S-transferase is used to create the GST gene fusion system in genetic engineering. Here, GST is used to purify and detect proteins of interest.