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Catalase is a common enzyme found in nearly all living organisms which are exposed to oxygen, where it functions to catalyze the decomposition of hydrogen peroxide to water and oxygen.[1] Catalase has one of the highest turnover numbers of all enzymes; one molecule of catalase can convert millions of molecules of hydrogen peroxide to water and oxygen per second.[2] 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.[7] Catalase was first noticed as a substance in 1818 when Louis Jacques Thénard, who discovered H2O2 (hydrogen peroxide), suggested that its breakdown is caused by a substance. In 1900, Oscar Loew was the first to give it the name catalase, and found its presence in many plants and animals.[8] In 1937 catalase from beef liver was crystallised by James B. Sumner[9] and the molecular weight worked out in 1938.[10] In 1969 the amino acid sequence of bovine catalase was worked out.[11] Then in 1981, the 3D structure of the protein was revealed.[12]
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