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. Most catalases exist as tetramers of 65KD subunits containing a protoheme IX group buried deep inside the structure. In eukaryotic cells, catalases are located in peroxisomes.