InterPro: IPR000763 Catalase-peroxidase haem

Haem-containing catalase-peroxidases are bifunctional antioxidant enzymes that exhibit both catalase (EC:1.11.1.6) and peroxidase (EC:1.11.1.7) activity, and which are present in many fungal, archaeal and bacterial species. These enzymes provide protection against oxidative stress by neutralising hydrogen peroxide, and are closely related to plant peroxidases [1]. They do not share sequence similarity with mono-functional, haem-containing catalases (IPR002226) that are ubiquitous in aerobic organisms, nor with non-haem manganese-containing catalases found in bacteria (IPR007760) [2]. Catalases convert two hydrogen peroxide molecules into water and molecular oxygen in a two-step reaction cycle that uses the two hydrogen peroxide molecules to alternately oxidise and reduce the haem iron. Peroxidases use hydrogen peroxide to oxidise the haem iron, but use different hydrogen donors such as NADH to then reduce the haem.

The structure of the catalase-peroxidase from the archaeon, Haloarcula marismortui, reveals a dimer of two identical subunits [3], although some catalase-peroxidases exist as homotetramers. The general topology, as well as the arrangement of the catalytic residues and haem in the active site, are similar to other class I peroxidases. However, the location of the haem group deeply buried inside the domain is typical of a catalase. The primary structure of the subunit can be divided into two similar halves, which may have arisen from a gene duplication event.