SOD Activity Assay Kit (Colorimetric) is a sensitive kit using WST-1 that produces a water-soluble formazan dye upon reduction with superoxide anion. The rate of the reduction with a superoxide anion is linearly related to the xanthine oxidase (XO) activity, and is inhibited by SOD. Therefore, the inhibition activity of SOD can be determined by a colorimetric method.
 
Specifically, one unit of SOD corresponds to the amount of enzyme needed to exhibit 50% dismutation of the superoxide radical.
 
Superoxide dismutases (SODs) are metallo enzymes that catalyse the dismutation of the superoxide anion to molecular oxygen and hydrogen peroxide. Thus, it forms a crucial part of the cellular antioxidant defense mechanism. This SOD Activity Assay Kit uses a tetrazolium salt for detection of superoxide radicals. Particularly, xantine oxidase and hypoxantine are the enzymes that generate these radicals.

Excessive reactive oxygen species, especially superoxide anion (O2•−), play important roles in the pathogenesis of many cardiovascular diseases, including hypertension and atherosclerosis. Superoxide dismutases (SODs) are the major antioxidant defense systems against O2•−. There are three isoforms of SOD in mammals: the cytoplasmic Cu/ ZnSOD (SOD1), the mitochondrial MnSOD (SOD2), and the extracellular Cu/ZnSOD (SOD3). These enzymes require catalytic metal (Cu or Mn) for their activation.