Glutathione S-transferases are a family of eukaryotic and prokaryotic phase II metabolic isozymes best known for their ability to catalyze the conjugation of the reduced form of glutathione to xenobiotic substrates for the purpose of detoxification. The GST family consists of three super-families: the cytosolic, mitochondrial, and microsomal (also known as MAPEG proteins). Based on their biochemical, immunologic and structural properties, the soluble GSTs are categorized into 4 main classes: alpha, mu, pi, and theta.