Glutathione reductase, activities exposure

Observations Table 1 shows the activity of the antioxidant enzymes of tomato roots after 72 h of exposure of allelochemical stress caused by S. deppei. Catalase (CAT) activity increases by 1.5 fold Ascorbate Peroxidase (APX) decreases 2.3 fold Glutathione reductase (GR) activity does not change with the treatment and Superoxide dismutase (SOD) decreases 1.3 fold. 

Subchronic exposure to MnCb for 7 days (total dose 1750 pmol/kg) by means of mini-osmotic pumps inplanted s.c. produced significant reduction in GSH-peroxidase (EC 1.11.1.9) activity in the cytosol and mitochondrial fractions of the whole rat brain and the striatum (Liccione and Maines 1988). The decrease in GSH-peroxidase was most pronounced in the mitochondrial fraction of the striatum where the activity was reduced to 35 % of the control. Catalase (EC 1.11.1.6) activity was also decreased in the striatum of rats treated with Mn but not in the whole brain. GSH content was markedly depleted (20 % of the control) in the striatum, although only modestly decreased in the whole brain (80% of the control). The treatment of rats with Mn also decreased the activity of oxidised glutathione reductase (EC 1.6.4.2) the same treatment increased the activity of y-glutamyltranspeptidase (EC 2.3.2.2). The activity of y-glutamylcysteine synthetase was not altered by Mn. 

As already discussed in chapter 4, reactive intermediates can react with reduced GSH either by a direct chemical reaction or by a GSH transferase-mediated reaction. If excessive, these reactions can deplete the cellular GSH. Also, reactive metabolites can oxidize GSH and other thiol groups such as those in proteins and thereby cause a change in thiol status. When the rate of oxidation of GSH exceeds the capacity of GSH reductase, then oxidized glutathione (GSSG) is actively transported out of the cell and thereby lost. Thus, reduced GSH may be removed reversibly by oxidation or formation of mixed disulfides with proteins and irreversibly by conjugation or loss of the oxidized form from the cell. Thus, after exposure of cells to quinones such as menadione, which cause oxidative stress, GSH conjugates, mixed disulfides, and GSSG are formed, all of which will reduce the cellular GSH level. 

Little is known about the specific biochemical mechanism(s) by which selenium and selenium compounds exert their acute toxic effects. Long-term effects on the hair, skin, nails, liver, and nervous system are also well documented, and a general theory has been developed to explain the toxicity of exposure to excess selenium, as discussed below. Generally, water-soluble forms are more easily absorbed and are generally of greater acute toxicity. Mechanisms of absorption and distribution for dermal and pulmonary uptake are unknown and subject to speculation, but an active transport mechanism for selenomethionine absorption in the intestine has been described (Spencer and Blau 1962). The mechanisms by which selenium exerts positive effects as a component of glutathione peroxidase, thioredoxin reductase, and the iodothyronine 5 -deiodinases are better understood, but the roles of other selenium-containing proteins in mammalian metabolism have not been clarified. 

Isothiocyanates are potent inducers of Phase II detoxification enzymes, such as quinone reductase and glutathione transferase (Faulkner et al. 1998 Fahey and Talalay 1999 Rose et al. 2000 Basten et al. 2002 Munday and Munday 2004). The induction of these enzymes enables the excretion of potential carcinogens prior to harmftil effects and is thought to be an effective mechanism to reduce the risk of carcinogenesis. The mechanism by which this occurs is likely to be by the activation of the transcription factors Nrl2. Upon exposure to... 

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