Tetranitroblue tetrazolium chloride

3,3′-(3,3′-Dimethoxy-4,4′-biphenylene)bis[2,5-bis(p-nitrophenyl)-2H-tetrazolium chloride]; Tetranitrotetrazolium blue chloride; TNBT

Tetranitroblue tetrazolium chloride (TNBT) is a reagent that is used to measure the activity of enzymes in biological samples. TNBT can be used as a histological stain for myocardial infarcts and other areas of necrosis. It has been shown to be reactive with toll-like receptors, which are proteins that play a role in the immune response. The reaction mechanism of TNBT starts with its conversion to blue formazan crystals by peroxidase or other oxidizing enzymes. These crystals are reduced back to their original colorless form by reducing agents such as NADH or glutathione, which are present in most cells. This reduction process generates an electron that is then transferred to NAD+, forming NADH and releasing H2O2 as a byproduct.