<p>This entry represents nickel-dependent superoxide dismutase (NiSOD) (<db_xref db="EC" dbkey="1.15.1.1"/>), a SOD enzyme that uses nickel, rather than iron, manganese, copper, or zinc. All SOD enzymes catalyse the dismutation of toxic superoxide radical anions to oxygen and hydrogen peroxide in order to protect cells from oxidative damage. The catalytic cycle of NiSOD consists of two half-reactions, each initiated by the successive approach of substrate to the metal centre. The first (reductive) phase involves Ni(III) reduction to Ni(II), and the second (oxidative) phase involves the metal reoxidation back to its resting state [<cite idref="PUB00035719"/>]. NiSOD has a novel SOD fold and assembly, consisting of a hexameric assembly of 4-helix bundles of up-and-down topology, which contains a 9-residue nickel-hook structural motif that is critical for metal binding and catalysis [<cite idref="PUB00031358"/>]. A gene for a required protease (NiSOD maturation protease; <db_xref db="INTERPRO" dbkey="IPR014124"/>) is adjacent to the NiSOD gene. </p>