InterPro domain: IPR040333

Catalases ( 1.11.1.6 ) are antioxidant enzymes that catalyse the conversion of hydrogen peroxide to water and molecular oxygen, serving to protect cells from its toxic effects [ 1 ]. Hydrogen peroxide is produced as a consequence of oxidative cellular metabolism and can be converted to the highly reactive hydroxyl radical via transition metals, this radical being able to damage a wide variety of molecules within a cell, leading to oxidative stress and cell death. Catalases act to neutralise hydrogen peroxide toxicity, and are produced by all aerobic organisms ranging from bacteria to man. Most catalases are mono-functional, haem-containing enzymes, although there are also bifunctional haem-containing peroxidase/catalases ( IPR000763 ) that are closely related to plant peroxidases, and non-haem, manganese-containing catalases ( IPR007760 ) that are found in bacteria [ 2 ]. Based on a phylogenetic analysis, catalases can be classified into clade 1, 2 and 3. Clade 1 contains small subunit catalases from plants and a subset of bacteria; clade 2 contains large subunit catalases from fungi and a second subset of bacteria; and clade 3 contains small subunit catalases from bacteria, fungi, protists, animals, and plants [ 3 , 4 ].

Clade 3 catalases are the most abundant subfamily and are found in all three kingdoms of life; they have a relatively small subunit size of 43 to 75kDa, and bind a protoheme IX (heme b) group buried deep inside the structure. Clade 3 catalases also bind NADPH as a second redox-active cofactor. They form tetramers, and in eukaryotic cells, catalases are located in peroxisomes [ 5 , 6 ].

1. Mitochondrial catalase and oxidative injury. Cell. Mol. Life Sci. 10, 189-99
2. Diversity of structures and properties among catalases. Proteins 61, 192-208
3. Phylogenetic relationships among prokaryotic and eukaryotic catalases. Arch. Biochem. Biophys. 14, 951-8
4. Structure of the Clade 1 catalase, CatF of Pseudomonas syringae, at 1.8 A resolution. Antioxid. Redox Signal. 50, 423-36
5. Evolution of catalases from bacteria to humans. Mol. Biol. Evol. 10, 1527-48
6. Thirty years of heme catalases structural biology. null 525, 102-10