GLUTATHIONE TRANSFERASE (GST; EC 2.5.1.18) is a multifunctionalenzyme that plays an important role in cellular detoxification. GST protects cells against foreign compounds such as carcinogens and drugs by catalyzing the attachment of glutathione to the compounds electrophilic and/or hydrophobic sites. This Glutathione S-transferase assay kit is based on the GST enzyme reaction between GSH and the GST substrate, CDNB (1-chloro-2,4-dinitrobenzene). The GST catalyzed formation of GS-DNB produces a dinitrophenyl thioether which can be detected spectrophotometrically at 340 nm. The rate of increase in absorbance at 340 nm is directly proportional to the GST activity in the sample.