*4.1.2 Catalase (CAT)*

Catalase (EC 1.11.1.6) is an enzyme responsible for H2O2 degradation that is generated by oxidases involved in β-oxidation of fatty acids, respiration, and purine catabolism [3]. It is present in nearly all animal cells as a protective enzyme. The highest levels of CAT activity are measured in the liver, kidney, and red blood cells.

Human CAT composes four identical subunits of 62 kDa, each subunit containing four distinct domains and one prosthetic heme group, and has a molecular mass of about 240 kDa [30]. CAT enzyme reacts with H2O2 to form water and molecular oxygen and with H donors such as methanol, ethanol, formic acid, or phenols with peroxidase activity. CAT protects cells from H2O2 generated within them. Therefore, it has an essential role in the acquisition of tolerance to oxidative stress in the adaptive response of cells. Various disease conditions and abnormalities are associated with the deficiency or mutation of CAT enzyme [30, 31].

#### *4.1.2.1 Application*

In the food industry, CAT enzyme is used to remove H2O2 from milk prior to cheese production, and to prevent food from oxidizing in food wrappers. In addition, CAT enzyme is used in the textile industry for H2O2 removal from fabrics, to make sure the material is peroxide free. Recently, esthetics industries have begun to use CAT enzyme in facial masks, as the combination of CAT enzyme with H2O2 on the face can be used to increase cellular oxygenation in the upper layers of the epidermis [3].
