Catalase activates the decomposition of hydrogen peroxide, a reactive oxygen species, into water and oxygen.

• Enzyme Commission Number: E.C. 1.11.1.6

It functions as a natural antioxidant, protecting cells against oxidative damage to proteins, lipids and nucleic acids. It has also been used to study the role reactive oxygen species play in gene expression and apoptosis.

Unit definition: one unit is defined as the amount of enzyme that will decompose 1 μmole of H₂O₂ per minute at 25 °C, pH 7,0.