The thioredoxin (Trx) system, which is composed of thioredoxin reductase (TrxR), thioredoxin and NADPH, is a key antioxidant system in defense against oxidative stress. Thioredoxin reductase (TrxR) is a ubiquitous enzyme which is also involved in many other cellular processes such as cell growth, p53 activity, cancer, immune response and viral infection.
The PromoKine Thioredoxin Reductase Activity Assay Kit provides a convenient colorimetric assay for detecting TrxR activity in various samples. In the assay TrxR catalyzes the reduction of 5, 5’-dithiobis (2-nitrobenzoic) acid (DTNB) with NADPH to 5-thio-2-nitrobenzoic acid (TNB2-), generating a strong yellow color (λmax = 412 nm). In crude biological samples, other enzymes such as glutathione reductase and glutathione peroxidase can also reduce DTNB. Therefore, a TrxR specific inhibitor is utilized to determine TrxR-specific activity and two assays are performed: The first measurement quantifies the total DTNB reduction by the sample, and the second one measures the DTNB reduction by the sample in the presence of the TrxR-specific inhibitor. The difference between the two results is the DTNB reduction by TrxR.