Identification and characterization of a selenium-dependent glutathione peroxidase in Setaria cervi Anchal Singh, Sushma Rathaur * Department of Biochemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005, UP, India Received 12 March 2005 Available online 13 April 2005 Abstract Setaria cervi a bovine filarial parasite secretes selenium glutathione peroxidase during in vitro cultivation. A significant amount of enzyme activity was detected in the somatic extract of different developmental stages of the parasite. Among different stages, micro- filariae showed a higher level of selenium glutathione peroxidase activity followed by males then females. However, when the activity was compared in excretory secretory products of these stages males showed higher activity than microfilariae and female worms. The enzyme was purified from female somatic extract using a combination of glutathione agarose and gel filtration chromatography, which migrated as a single band of molecular mass 20 kDa. Selenium content of purified enzyme was estimated by atomic absorp- tion spectroscopy and found to be 3.5 ng selenium/lg of protein. Further, inhibition of enzyme activity by potassium cyanide sug- gested the presence of selenium at the active site of enzyme. This is the first report of identification of selenium glutathione peroxidase from any filarial parasite. Ó 2005 Elsevier Inc. All rights reserved. Keywords: Selenium; Glutathione peroxidase; Bovine parasite; Setaria cervi Human filariasis is a chronic debilitating disease, which causes extensive morbidity and little mortality. Three species of filarial worms, Wuchereria bancrofti, Brugia malayi, and Brugia timori, are the causative agents of lymphatic filariasis in humans, defined by the characteristic tropism of adult worms of each species for the afferent lymphatic. Reproductive activity leads to the release of a large number of microfilariae, which circulate in vascular system and upon ingestion by an appropriate mosquito vector develop to infective third stage larvae (L 3 ) within 10–15 days. After a subsequent blood meal, the infective larvae enter the definitive host via the wound and mature to adult stage over several months involving two moults, during which the entire nematode exoskeleton is replaced. These filarial para- sites are long lived and by still unknown mechanisms they suppress the hostÕs immune response. The major immune effector mechanisms involve var- ious types of cells (macrophages, leukocytes, and plate- lets) potentiated by antibodies and cytokines [1]. One mechanism that cells may employ to kill parasites is the release of toxic products, molecules, and oxygen rad- icals during the respiratory burst or nitric oxide release [2–4]. Toxic proteins among other things can attack the parasite lipid membrane and breach its integrity [5]. The oxygen radicals released, which include O 2  , H 2 O 2 , singlet oxygen (O 2 ), and hydroxyl radicals (OH Å ) can damage cell membranes, unfold or inactivate proteins, degrade nucleic acid, kill cells and eventually the parasite. To establish and maintain itself in the vasculature of the host, the parasite has evolved a number of immune evasion mechanisms [6,7] including the production of antioxidant enzymes like superoxide dismutase (SOD), 0006-291X/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2005.03.235 * Corresponding author. Fax: +091 0542 2368174. E-mail address: sushmarathaur@yahoo.com (S. Rathaur). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 331 (2005) 1069–1074 BBRC