This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
Amino acid responsible for Thioredoxin reductase activation: 
Select and explain. 
A. Serine, B. Selenocysteine, C. Cysteine, D. Alanine
B: Selenocysteine
Answer: B: Selenocysteine 
Explanation: Ans. B. SelenocysteineSelenocysteine is seen in the active site of following Enzymes and ProteinsQThioredoxin reductaseGlutathione PeroxidaseIodothyronine DeiodinaseSelenoprotein P