Glutathione GSH peroxidase

Although inorganic selenium does not have antioxidant properties, selenium has an important role in cellular antioxidant defenses as a necessary component of selenoproteins. Selenium is incorporated into selenoproteins as selenocysteine. The glutathione (GSH) peroxidases are the best-characterized selenoproteins, although other circulating selenoproteins also have antioxidant functions. 

Glutathione (GSH) peroxidase (EC 1.11.1.9) is one of several selenoproteins that contain a unique selenocysteine residue at the active site (1). This enzyme catalyzes the GSH-dependent reduction of both hydrogen peroxide and organic hydroperoxides, including fatty acid hydroperoxides formed during lipid peroxidation. GSH peroxidase activity has been measured in both protozoan and helminth parasites (11,12). The enzyme from Schistosoma mansoni has been cloned (13). The presence of the unique selenocysteine codon (UGA) confirms that it is a selenoprotein. Although GSH peroxidase activity appears to be absent from Hymenolepsis dimimta and M. expansa... 

Antioxidants are chemical compoimds that can bind to free radicals and thus prevent them from damaging healthy cells. Antioxidants can be divided into enzymatic and non-enzymatic subtypes. Several antioxidant enzymes are produced by the body, with the three major classes being catalase, the glutathione (GSH) peroxidases, and the superoxide dismutases (SODs). Non-enzymatic antioxidants include the irmate com-poimd glutathione as well as antioxidant vitamins obtained through the diet, such as a-tocopherol (vitamin E), ascorbic acid (vitamin C), and P-carotene. 

Glutathione redox cycle consists of NADPH, reduced glutathione GSH, glutathione reductase (GR), and glutathione peroxidase (GP) (Reactions (7) and (8)) ... 

The acid-soluble SH-groups in platelets are mainly those of glutathione (GSH). GSH is a cofactor for enzymes such as peroxidase. If feverfew is able to interfere with this cofactor, enzyme function may be impaired. One pathway that may be affected in this way is the metabolism of arachidonic acid (Figure 6.1). In the presence of feverfew extract an increase was found in lipoxygenase product formation and impaired conversion of HPETE to HETE, for which GSH is a cofactor [52]. Inhibition of the liberation of [ " C]arachidonic acid from phospholipids was also found [53], which implies impairment of phospholipase A2 activity and for which SH-groups are thought to be important. 

Lipid peroxidation activity. Solubilized green tea, administered orally to rats for 5 weeks, reduced lipid peroxidation products. The treatment produced increased activity of glutathione (GSFf) peroxidase and GSH reductase, increased content of reduced GSH, a marked decrease in lipid hydroperoxides and malondialdehyde in the liver, an increase in the concentration of vitamin A by about 40%. A minor change in the measured parameters was observed in the blood... 

ROS are maintained at tolerable levels through the combined efforts of antioxidant mechanisms, which include both enzymes and nonenzymatic molecules. Important antioxidant enzymes include superoxide dismutases (SODs), catalases (CATs), peroxidases, and those maintaining reduced glutathione (GSH) levels. Nonenzymatic antioxidants include GSH, a tripeptide containing a cysteinamino acid, and vitamins, such as vitamin A, E, and C. 

Glutathione GSH Lipid bilayer of all Vitamin C peroxidase Cellular membranes... 

The G-6-PD is a large structure with many genetic variants perhaps more than any other human protein (59-62). It is an almost ubiquitous cytosolic enzyme which catalyzes the first step in the hexose monophosphate pathway (62). Its most essential function is to produce the NADPH required to maintain the concentration of reduced glutathione (GSH) in the face of oxidative stress. The GSH together with catalase and glutathione peroxidase represent the defence against hydrogen peroxide, and this is particularly true in red blood cells. 

Devasena and Menon (2007) reported that fenugreek seeds had a modulatory effect on colon tumour incidence, as well as hepatic lipid peroxidation (LPO) during DMH (1,2-dimethylhydrazine) colon carcinogenesis in male Wistar rats. In DMH-treated rats, 100% colon tumour incidence was accompanied by enhanced LPO and a decrease in reduced glutathione (GSH) content, as well as a fall in glutathione peroxidase (GPx), glutathione S-transferase (GST), superoxide dismutase (SOD) and catalase (CAT) activities. Inclusion of fenugreek seed powder in the diet of DMH-treated rats reduced the colon tumour incidence to 16.6%, decreased the lipid peroxidation and increased the activities of GPx, GST, SOD and CAT in the liver. 

---