Diversity
Two classes of thioredoxin reductase have evolved independently:
- A high molecular weight (MW = ~55,000) type containing a selenocysteine residue in its active site has been identified in higher eukaryotes including humans. This TxR is related to glutathione reductase, trypanothione reductase, mercuric reductase and lipoamide dehydrogenase.
- A low molecular weight (MW = ~ 35,000) type has been identified in archaea, bacteria and other eukarya.
These two classes of TrxR have only ~20% sequence identity in the section of primary sequence where they can be reliably aligned. The net reaction of both classes of TrxR is identical but the mechanism of action of each is distinct.
Humans express three thioredoxin reductase isozymes: TrxR1 (cytosolic), TrxR2 (mitochondrial), TrxR3 (testis specific). Each isozyme is encoded by a separate gene:
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Read more about this topic: Thioredoxin Reductase
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