Thioredoxin Reductases

Thioredoxin reductase (TrxR), or thioredoxin disulfide reductase (EC 1.8.1.9), is a component of the thioredoxin system, along with NADPH and thioredoxin, which is critical for maintaining redox function and preventing oxidative stress.

There are two TrxR variants, low molecular weight TrxR (L-TrxR), a 70-kDa protein present in bacteria, fungi and plants, and high molecular weight TrxR (H-TrxR), a 112-130 kDa protein found in higher eukaryotes. In mammals there are three isoforms of H-TrxR: TrxR1, found in the cytoplasm; TrxR2, found in mitochondria; and TrxR3 (also known as thioredoxin glutathione reductase or TGR), found only in specialized tissues, such as the testis.

The enzyme is a member of the pyridine nucleotide-disulfide oxidoreductase family, which includes glutathione reductase, many of which have the same N-terminal active site motif, CVNVGC. Mammalian TrxR contains a selenocysteine residue in the C-terminal motif, which is conserved across species and is essential for catalytic activity. TrxR is a homodimeric enzyme, which in conjunction with NADPH, functions to reduce the active site disulfide of thioredoxin to a dithiol. It also has a broad range of other substrates, including protein disulfide isomerase (PDI), glutaredoxin2 and lipoic acid. The enzyme has two catalytically important redox sites, one comprising flavin adenine dinucleotide (FAD) and nearby Cys residues, which receives electrons from NADPH, and the other consisting of the C-terminal motif that receives electrons from the other catalytic site and transfers them to Trx.

The thioredoxin system is ubiquitous across species, and in mammals it works in conjunction with the glutathione system to control the cellular redox environment. TrxR is involved in all biochemical pathways in which Trx has a role as a reducing substrate, and as such is of interest in multiple physiological and pathological processes, including apoptosis, cancer, autoimmune diseases, chronic inflammation and neurodegenerative disorders. TrxR and Trx are overexpressed in many cancers, with cancer cell growth being dependent on the Trx system, so TrxR may be a target for cancer therapy. In addition a number of bacteria, including Mycobacterium tuberculosis and Helicobacter pylori are lacking the glutathione antioxidant system making TrxR a potential target for antibacterials.

External sources of pharmacological information for Thioredoxin Reductases :

• BJP Guide

Literature for Thioredoxin Reductases

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Autophagy Poster

Autophagy is a cellular process used by cells for degradation and recycling. Written by Patricia Boya and Patrice Codogno, this poster summarizes the molecular machinery, physiology and pathology of autophagy. Compounds available from Tocris are listed.

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Programmed Cell Death Poster

There are two currently recognized forms of programmed cell death: apoptosis and necroptosis. This poster summarizes the signaling pathways involved in apoptosis, necroptosis and cell survival following death receptor activation, and highlights the influence of the molecular switch, cFLIP, on cell fate.

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Thioredoxin Reductase Gene Data