Catalase: A repertoire of unusual features.

Catalases are antioxidant enzymes which catalyze the breakdown of hydrogen peroxide to water and oxygen, and are one of the oldest enzymes to be studied biochemically. The first crystal structure of a catalase appeared in the year 1980 and it revealed the tetrameric nature of the enzyme and presence of channels accessing the deeply buried active site heme. An interesting feature of the tetrameric structure is the characteristic interweaving or arm exchange of the subunits. The recent elucidation of the crystal structure of transport proteins (porins, aquaporins) showed that these proteins are also tetrameric in nature and posses channels. However, recent specific investigations focusing on the roles for these channels, in the mechanism of enzyme action of catalases, revealed significant similarities with that observed for the transport of water and/or glycerol, in aquaporins.