Thioredoxin reductase

Thioredoxin Reductase (TR, TrxR) are the only known enzymes to reduce thioredoxin (Trx).

Diversity
All known kingdom of organisms contain thioredoxin reductase. Two types of thioredoxin reductase evolved independently:
 * prokaryotes, archaea and most plants have one type.
 * higher eukaryotes and some plants contain a different one that contains selenocysteine.

Three TRs exist in animals: TR1, TR3, and TGR. Both TR1 and TR3 are essential proteins for mouse embryogenesis.

Clinical significance
Since the activity of this enzyme is essential for cell growth and survival, it is a good target for anti-tumor therapy.

For example, motexafin gadolinium (MGd) is a new chemotherapeutic agent that selectively targets tumor cells, leading to cell death and apoptosis via inhibition of thioredoxin reductase and ribonucleotide reductase.