Application

Thioredoxin Reductase from rat liver can be used for studying the uptake and reduction of a-lipoic acid by utilizing reducing capacity of human erythrocytes. The product can also be used for studying the activation mechanism of transglutaminase 2 (TG2) in the extracellular matrix by using Thioredoxin.

Biochem/physiol Actions

Thioredoxin Reductase is a ubiquitous enzyme that catalyzes the active site disulfide of thioredoxin by NADPH. The product also reduces ubiquinone and regenerates ubiquinol, a powerful antioxidant.

Thioredoxin reductase (TrxR) is a NADPH-dependent oxidoreductase containing one FAD per subunit that reduces the active site disulfide in oxidized thioredoxin (Trx). The molecular weight of the isozymes from mammalian sources vary between 55-67 kDa as compared with 35 kDa in prokaryotes, plants or yeast. The substrate specificity of the mammalian enzyme is much broader than the prokaryotic enzyme reducing both mammalian and E. coli thioredoxins as well as non-disulfide substrates such selenite, lipoic acids, lipid hydroperoxides, and hydrogen peroxide.

Thioredoxin reductase from mammalian sources contains a selenocysteine residue that is essential for the activity of the enzyme. It is one of the antioxidant enzymes present in the mammalian cell together with catalase, glutathione peroxidase and superoxide dismutase, and helps in removal of reactive oxygen species (ROS) from the cell. An example is the removal of excess nitric oxide (NO) by the formation of a complex with glutathione forming the S-nitroso-glutathione adduct (GS-NO). This can be cleaved directly by thioredoxin reductase. Hydrogen peroxide, another deleterious oxidant in the cell, is also reduced directly by mammalian TrxR.

Unit Definition

One unit will cause an increase in absorbance of 1.0 at 412 nm (when measured in a non-coupled assay containing DTNB [Sigma No. D8130] alone as substrate) per minute at pH 7.0 at 25 Â°C.