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
Selenocysteine is associated with ? 
Select and explain. 
A. Carbonic anhydrase, B. Catalase, C. Deiodinase, D. Transferase
C: Deiodinase
Answer: C: Deiodinase 
Explanation: Selenocysteine is considered as 21 standard amino acid.It is present at the active site of some enzymes that catalyze redox reactions, e.g. thioredoxin reductase, glutathione peroxidase, and the deiodinase (conves thyroxin to triiothyronine).