Thioredoxin reductases are the only known enzymes to reduce thioredoxin. Two classes of thioredoxin reductase have been identified: one class in bacteria and some eukaryotes and one in animals. Both classes are flavoproteins which function as homodimers. TRXB (Thioredoxin reductase) is a ubiquitous enzyme which is involved in many cellular processes such as cell growth, p53 activity, and protection against oxidation stress