The glutathione-S-transferases (GST) are important phase II detoxification enzymes found mainly in the cytosol, and are involved in the detoxification of drugs and harmful chemicals in the body (112). They are found in very high concentrations in the liver, where they conjugate glutathione to the electrophilic centers of lipophilic compounds and increase their solubility in order to facilitate their excretion (113,114) (Figure 10.7). GST posses a wide range of substrate specificities and can catalyze the reduction of breakdown products of macromolecules formed as a result of oxidative stress including reactive unsaturated carbonyls, oxidized DNA bases, and hydroperoxides, and therefore play a vital role in protecting tissues against oxidative damage and oxidative stress (112-115). As a result of the beneficial functions of GST it serves as an important biomarker for oxidative stress (115). Most of the methods to assay the GST activity involve measuring the conjugation of 1-chloro-2,4-dinitrobenzene (CDNB) with reduced glutathione (114). The conjugation of GSH with CDNB results in an increase in absorbance at 340 nm which is measured spectrophotometrically. The rate of increase is directly proportional to the GST activity in the sample. This assay can also be used to measure GST activity in plasma, cell lysates and tissue homogenates (114).
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