Glutathione S-transferases. The first enzymatic step in mercapturic acid formation.

Levels of glutathione, glutathione reductase and glutathione S-transferase activities in rat lung and liver.

The glutathione S-transferases (GST) represent a major group of detoxification enzymes. All eukaryotic species possess multiple cytosolic and membrane-bound GST isoenzymes, each of which displays distinct catalytic as well as noncatalytic binding properties: the cytosolic enzymes are encoded by at least five distantly related gene families (designated class alpha, mu, pi, sigma, and theta GST), whereas the membrane-bound enzymes, microsomal GST and leukotriene C, synthetase, are encoded by single genes and both have arisen separately from the soluble GST. Evidence suggests that the level of expression of GST is a crucial factor in determining the sensitivity of cells to a broad spectrum of toxic chemicals. In this article the biochemical functions of GST are described to show how individual isoenzymes contribute to resistance to carcinogens, antitumor drugs, environmental pollutants, and products of oxidative stress.A description of the mechanisms of transcriptional and posttranscriptional regulat...

The glutathione S-transferase supergene family: regulation of GST and the contribution of the isoenzymes to cancer chemoprotection and drug resistance.

Publisher Summary This chapter provides the spectrophotometric, titrimetric, nitrite, and cyanide assay for the differentiation of glutathione S-transferases. Spectrophotometric assays depend upon a direct change in the absorbance of the substrate when it is conjugated with glutathione (GSH). Because each of the reactions is catalyzed at a finite rate in the absence of enzyme, care is needed to reduce nonenzymatic catalysis by minimizing substrate concentrations and by decreasing pH wherever necessary. Titrimetric assay is based on the principle that the conjugation of alkyl halides with GSH can be measured titrimetrically. Although acid production accompanies many of the transferase catalyzed reactions in which thioethers are formed, titrimetry is only used when more convenient assays are not available. Nitrite assay is based on the principle that nitrite is released when GSH reacts with nitroalkanes or with organic nitrate esters. The nitrite can be assayed as the limiting factor in a diazotization reaction with sulfanilamide that produces a readily quantitatable pink dye. Cyanide assay is based on the fact that when glutathione transferases catalyze the attack of the glutathione thiolate ion on the electrophilic sulfur atom of several organic thiocyanates, it results in the formation of an asymmetric glutathionyl disulfide and cyanide. Cyanide can be readily quantitated by a calorimetric method.

Assays for differentiation of glutathione S-transferases.

The discovery that there is a close relationship between ascorbate and glutathione dates from soon after the characterization of the chemical formulae of the two molecules ([Szent-Gyorgyi, 1931][1]; [Hopkins and Morgan, 1936][2]). Similarly, it has long been known that thylakoids can generate

William B. Jakoby

Papers

Glutathione S-transferases. The first enzymatic step in mercapturic acid formation.

Mechanism for the several activities of the glutathione S-transferases.

The enzymes of detoxication

The Enzymes of Detoxication

Glutathione S-transferase A. A novel kinetic mechanism in which the major reaction pathway depends on substrate concentration.