Catalase is an enzyme present in blood and other tissues with antioxidant activity. 
This Catalase Activity Assay Kit consist on a reaction giving rise to a compound that forms a complex with the chromogen. This reaction produces a purple color directly proportional to catalase activity that can be determined by means of a simple and fast spectrophotometrical measure.
 
Information

Hydrogen peroxide is a reactive oxygen specie (ROS). It is a toxic product of normal aerobic metabolism and pathogenic ROS production, involving oxidase and superoxide dismutase reactions. Hydrogen peroxide is poisonous to eukaryotic cells. Particularly, in high doses, it can initiate oxidation of DNA, lipids, and proteins, which can lead to mutagenesis and cell death.
On the other hand, catalase is an antioxidant enzyme omnipresent in mammalian and non-mammalian cells. Particularly, the reaction that they catalyze is the destruction of hydrogen peroxide by dismutation. Eukaryotic catalases are heme enzymes, which are present in the liver, kidney, and erythrocytes in high concentrations. However, the lowest concentrations are in the connective tissues.

This enzyme catalyzes the reaction that consumes hydrogen peroxide, transforming it into water and oxygen. Since it is difficult to directly measure hydrogen peroxide in biological samples, the determination of these detoxifying enzymes has substituted this procedure. In addition, Catalase activity levels are also related to antioxidant capacity.