Formazan

Formazan dyes are artificial chromogenic products of the reduction of tetrazolium salts by dehydrogenases and reductases. They have a variety of colors from dark blue to deep red to orange, depending on the original tetrazolium salt used as the substrate for the reaction.

Leading examples of tetrazolium salts, include:[1]

  1. INT (2-(4-Iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride), (water insoluble)
  2. MTT (3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2H-tetrazolium bromide) (used in the MTT assay), (water insoluble)
  3. XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) (water soluble)
  4. MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) (used in the MTS assay) (water soluble).
  5. TTC or Tetrazolium chloride (2,3,5-Triphenyl-2H-tetrazolium chloride) (water soluble)

When reduced in a cell, either enzymatically or through direct reaction with NADH or NADPH the classical tetrazolium salt, MTT, turns bright blue and may form an insoluble precipitate. These formazan dyes are commonly used in cell proliferation and toxicity assays like the EpiSkin test since they only stain living cells.[2][3]

References

  1. ^ Altman FP (1976). "Tetrazolium salts and formazans". Prog Histochem Cytochem 9 (3): 1–56. PMID 792958. 
  2. ^ Marshall NJ, Goodwin CJ, Holt SJ (June 1995). "A critical assessment of the use of microculture tetrazolium assays to measure cell growth and function". Growth Regul. 5 (2): 69–84. PMID 7627094. 
  3. ^ Scudiero DA, Shoemaker RH, Paull KD, et al. (1 September 1988). "Evaluation of a soluble tetrazolium/formazan assay for cell growth and drug sensitivity in culture using human and other tumor cell lines". Cancer Res. 48 (17): 4827–33. PMID 3409223. http://cancerres.aacrjournals.org/cgi/pmidlookup?view=long&pmid=3409223.