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    Characterization of an interesting selenium-dependent glutathione peroxidase (Se-GPx) protecting cells against environmental stress: The Camelus dromedarius erythrocytes Se-GPx
    (Elsevier Ltd, 2019) Chafik A.; Essamadi A.; Çelik S.Y.; Solak K.; Mavi A.
    Camel lives most of its life under high environmental stress in the desert. Glutathione peroxidase plays a key role in protecting cells against oxidative stress. For the first time, selenium-dependent glutathione peroxidase (Se-GPx) was purified from camel erythrocytes, biochemically characterized, and some of its properties were studied. The enzyme was purified using ethanol-chloroform treatment, acetone precipitation and ion exchange chromatography. A purification fold of 33.72 with 0.19% yield were obtained. The native molecular weight of the enzyme was estimated to be about 69 kDa. On SDS-PAGE, the enzyme was composed of two different subunits with a molecular weight of approximately 53 and 21 kDa. An optimum temperature of 47 °C and an optimum pH of 7.2 were found. The activation energy was 41.71 kJ/mol. This enzyme was inhibited by thiol reagents, D,L-Dithiothreitol and ?-Mercaptoethanol, and was sensitive to bivalent cations. The enzyme had a general specificity toward hydroperoxides, and high specificity for reduced glutathione. The purified enzyme contained 3.06 mol of selenium per mol of protein. The Km and Vmax values for hydrogen peroxide and reduced glutathione were 0.72 and 1.58 mM, and 25.33 and 31.03 U/mg, respectively. The biochemical properties of camel Se-GPx were different comparing to those of mammalian species. Lower molecular weight, heterodimeric structure, higher optimum temperature, relatively lower optimum pH, lower content of selenium and higher affinity for hydrogen peroxide at low reduced glutathione concentration, these could be explained by the fact that camel is able to live in the intense environmental stress in the desert. © 2019 Elsevier Ltd
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    Partial Purification and Some Interesting Properties of Glutathione Peroxidase from Liver of Camel (Camelus dromedarius)
    (Pleiades Publishing, 2018) Chafik A.; Essamadi A.; Çelik S.Y.; Solak K.; Mavi A.
    Climate change and increasing temperatures are global concerns. Well adapted to desert life, the camel (Camelus dromedarius) lives most of its life under high environmental stress and represents an ideal model for studying desert adaptation among mammals. Glutathione peroxidase is the principal antioxidant defense system capable of protecting cells from oxidative stress. Glutathione Peroxidase from camel liver was purified (11.64-fold purification with 1.73% yield) and characterized The molecular weight of the enzyme was estimated to be about 69 kDa by gel filtration and 34 kDa by SDS-PAGE, implying dimeric structure of the protein. An optimum temperature of 47°C and an optimum pH of 7.8 were found. This enzyme is a typical SH-enzyme that is inhibited by D,L-dithiothreitol and ?-mercaptoethanol and sensitive to bivalent cations. The enzyme had common specificity toward hydroperoxides and high specificity for reduced glutathione. The Km and Vmax values for hydrogen peroxide and reduced glutathione were 0.57 and 2.10 mM and 1.11 and 0.87 U/mg, respectively. The purified enzyme contained 16 ng of selenium per mg of protein. Our results show that the camel glutathione peroxidse exhibits properties different of those reported for other mammalian species. Lower molecular weight, homodimeric structure, higher optimum temperature, relatively low optimum pH, high affinity for hydrogen peroxide at low concentration of reduced glutathione and very low content of selenium could be explained by adaptation of the camel to living in the desert under intense environmental stress. © 2018, Pleiades Publishing, Ltd.