noun, plural: catalases
A catalase is an ubiquitous enzyme as it occurs in nearly all living organisms. As an enzyme, it catalyzes the decomposition of hydrogen peroxide into oxygen and water. This function is essential to an organism. It protects the cell from oxidative damage as a result of overwhelming amounts of reactive oxygen species. Reactive oxygen species are byproduct of many metabolic processes of the cell. They are chemically reactive. Examples include peroxides, superoxides, singlet oxygen, and hydroxyl radical. In the presence of environmental stress, they could increase dramatically and lead to oxidative stress. To prevent the potential damage to cells and tissues, they need to be converted quickly. The cell, thus, use catalase to decompose them into less-reactive forms. One catalase can turn millions of hydrogen peroxide to water and oxygen in a second. The catalase is usually located in the peroxisome.
The catalase is a tetrameric protein. It is made up of four subunits. It has four iron-containing heme groups, which enables it to react with hydrogen peroxide. The reaction is as follows: 2 H2O2 → 2 H2O + O2