Probing variable axial ligation in nickel superoxide dismutase utilizing metallopeptide-based models: insight into the superoxide disproportionation mechanism.

Nickel superoxide dismutase (NiSOD) is a bacterial metalloenzyme that possesses a mononuclear Ni-center and catalyzes the disproportionation of O2*- by cycling between NiII and NiIII oxidation states. Herein we present evidence from several SOD active metallopeptide maquettes ([Ni(SODM2H(1)X)]; SODM2H(1)X = H2N-XCDLPCG-COOH; X = H, D, or A) that the Ni-center of NiSOD most likely remains five-coordinate during SOD catalysis using thin-film voltammetry. N3- and CN- titration studies suggest that O2*- disproportionation by [Ni(SODM2H(1)X)] proceeds via an outersphere mechanism.