SOD Assay Kit-WST

Superoxide dismutase (SOD), which catalyzes the dismutation of the superoxide anion (O2.-) into hydrogen peroxide and molecular oxygen, is one of the most important antioxidative enzymes. In mammals, cytosolic SOD has a greenish color and consists of two subunits, one containing copper and the other zinc (Cu/Zn-SOD). Mitochondrial and bacterial SOD has a reddish-purple color and contains manganese (Mn-SOD). E. coli has Mn-SOD and SOD containing iron (Fe-SOD). Several direct and indirect methods have been developed to determine SOD activity. An indirect method using nitrotetrazolium blue is often used because of its convenience. However, there are several disadvantages to this method, such as poor water solubility of the formazan dye and its reaction with the reduced form of xanthine oxidase. Although cytochrome C is also commonly used for SOD activity detection, its reactivity with superoxide is too high to determine low levels of SOD activity.SOD Assay Kit-WST allows a very convenient and highly sensitive SOD assay by utilizing Dojindo’s highly water-soluble tetrazolium salt, WST-1 (2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfo-phenyl)-2H-tetrazolium, monosodium salt), which produces a water-soluble formazan dye upon reduction with a superoxide anion. WST-1 is 70 times less reactive with superoxide anion than cytochrome C; therefore, highly sensitive SOD detection is possible and samples can be diluted with buffer to minimize background problems. WST-1 does not react with the reduced form of xanthine oxidase; therefore, even 100% inhibition with SOD is detectable. The rate of WST-1 reduction by superoxide anion is linearly related to the xanthine oxidase activity and is inhibited by SOD (see figure below). Therefore, the IC50 (50% inhibition concentration) of SOD or SOD-like materials can be determined using colorimetric methods.

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