Nickel containing superoxide dismutase (NiSOD) is a metalloenzyme containing a hexameric assembly of right-handed 4-helix bundles of up-down-up-down topology with an N-terminal His-Cys-X-X-Pro-Cys-Gly-X-Tyr motif that chelates the active site Ni ions. NiSOD catalyses the disproportionation of superoxide to peroxide and molecular oxygen through alternate oxidation and reduction of Ni, protecting cells from the toxic products of aerobic metabolism [1].

1: Nickel superoxide dismutase structure and mechanism. Barondeau DP, Kassmann CJ, Bruns CK, Tainer JA, Getzoff ED; Biochemistry. 2004;43:8038-8047. PMID:15209499