"Catalase is a common enzyme found in nearly all living organisms that are exposed to oxygen, where it 
catalyzes the decomposition of hydrogen peroxide to water and oxygen.[1] Catalase has one of the highest turnover numbers of all enzymes; one catalase molecule can convert 40 million molecules of hydrogen peroxide to water and oxygen each second."
"Catalase is a tetramer of four polypeptide chains, each over 500 amino acids long.[3] 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,[4] and has a fairly broad maximum (the rate of reaction does not change appreciably at pHs between 6.8 and 7.5).[5] The pH optimum for other catalases varies between 4 and 11 depending on the species.[6] The optimum temperature also varies by species."