Enzymes of the glutathione S-transferase (GST) family are composed of many cytosolic, mitochondrial, and microsomal (now designated as MAPEG) proteins. GSTs are present in eukaryotes and Gram-negative bacteria, where they catalyze a variety of reactions and accept endogenous and xenobiotic substrates. Examples of GST are Buthionine and Thiocarbamoyl.