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Selenium , as a constituent of glutathione peroxidase , plays a role in the antioxidant defense systems of the body , but other metabolic roles for selenium may yet be discovered .
 glutathione peroxidase
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 glutathione peroxidase