Catalase is a ubiquitous enzyme found in both prokaryotes and eukaryotes, which is involved in the protection of cells from the toxic effects of peroxides. It catalyzes the conversion of hydrogen peroxide to water and molecular oxygen. Catalases also utilize hydrogen peroxide to oxidize various substrates such as alcohol or phenols. 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 75 kDa, 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.
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