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

Ascorbate and glutathione: the heart of the redox hub.

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

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

The initial enzymic step in mercapturic acid formation is catalyzed by glutathione S-transferase. Several species of this enzyme, designated as transferases α. β, γ, δ and e an the basis of increasing isoelectric points, were isolated from human liver. Evidence is presented that each of the purified species is homogeneous with respect to sodium dodecylsulfate-gel electrophoresis. Transferases α, β and ɛ each appear as a single band an gel electrofocusing: transferases α and δ are present as two and three bands, respectively, with each band catalytically active. Amino acid analysis indicated the five transferases to be either very closely related or identical in this respect.



All enzyme species have a molecular weight of about 48 500 and consist of two apparently identical subunits. The spectrum of substrates is the same for each although the enzymes differ slightly in specific activity. As is the case for the rat liver enzymes, each of the human transferases binds bilirubin although this compound is not a substrate

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1975.tb20987.x

William H. Habig

Papers

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

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

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

Multiple Forms of Human Glutathione S-Transferase and Their Affinity for Bilirubin

Binding of nonsubstrate ligands to the glutathione S-transferases.