This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Glutathione reductase contains the following metal: 
Select and explain. 
A. Selenium, B. Magnesium, C. Manganese, D. Calcium
A: Selenium
Answer: A: Selenium 
Explanation: In red blood cells the pentose phosphate pathway provides NADPH for the reduction of oxidized glutathione catalyzed by glutathione reductase, a flavoprotein containing FAD. Reduced glutathione removes H2O2 in a reaction catalyzed by glutathione peroxidase, an enzyme that contains the selenium analogue of cysteine (selenocysteine) at the active site (Figure 21-3). The reaction is impoant, since accumulation of H2O2 may decrease the life span of the erythrocyte by causing oxidative damage to the cell membrane, leading to hemolysis Ref: Harper 28th edition, chapter 21.