Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals). It catalyzes the decomposition of hydrogen peroxide to water and oxygen.[3] It is a very important enzyme in protecting the cell from oxidative damage by reactive oxygen species (ROS). Likewise, catalase has one of the highest turnover numbers of all enzymes; one catalase molecule can convert millions of hydrogen peroxide molecules to water and oxygen each second.[4]
Catalase is a tetramer of four polypeptide chains, each over 500 amino acids long.[5] It contains four porphyrin heme (iron) groups that allow the enzyme to react with the hydrogen peroxide. The optimum pH for human catalase is approximately 7,[6] and has a fairly broad maximum (the rate of reaction does not change appreciably at pHs between 6.8 and 7.5).[7] The pH optimum for other catalases varies between 4 and 11 depending on the species.[8] The optimum temperature also varies by species.[9]