Enzymes which promote reactions involving the decompn of hydrogen peroxide to water and oxygen. Although widely distributed among animals, plants, bacteria, and fungi, catalase in mammalian liver and blood has been most intensively studied. Catalase for commercial use obtained from animal liver, bacterial (Micrococcus lysodeikticus), and fungal (Aspergillus niger) sources. Isoln from mammalian livers and kidneys: Lolli, Cavanaugh, US 2703779 (1955 to Armour); Schroeder et al., Biochim. Biophys. Acta 58, 611 (1962); Dan, US 2992167 (1961 to Chr. Hansen's Lab.); from Aspergillus niger: Faucett et al., US 3102081 (1963 to Miles Labs.). All catalases so far isolated contain four tetrahedrally arranged subunits of equal size giving an approximate mol wt of 240,000. Each subunit consists of a single polypeptide chain associated with a single prosthetic group, ferric protoporphyrin IX. Amino acid sequence of bovine liver catalase subunit: Schroeder et al., Arch. Biochem. Biophys. 131, 653 (1969). Bovine hepatocatalase, a term for catalase obtained from liver, was reported to lower serum cholesterol; the active form was found to contain a catalytic amount of zinc (0.32%): Azarnoff, Curran, J. Lab. Clin. Med. 60, 856 (1962), cf. Laporte et al., Biochem. Pharmacol. 11, 670 (1962). Reviews: Nicholls, Schonbaum, in The Enzymes vol. 8, P. D. Boyer et al., Eds. (Academic Press, New York, 1963) pp 147-225; Deisseroth, Daunce, Physiol. Rev. 50, 319 (1970); Schonbaum, Chance, in The Enzymes vol. 13 (part C), P. D. Boyer, Ed. (Academic Press, New York, 3rd ed., 1976) pp 363-408.