A Nickel Superoxide Dismutase Maquette That Reproduces the Spectroscopic and Functional Properties of the Metalloenzyme

Abstract

Described herein is a nickel superoxide dismutase (NiSOD) maquette ([Ni(SOD(M1))]) based on the first 12 residues from the N-terminal sequence of Streptomyces coelicolor NiSOD. The apopeptide (SOD(M1)) was prepared by standard solid-phase Fmoc peptide synthesis. SOD(M1) will readily coordinate Ni(II) in a 1:1 ratio in slightly basic aqueous sodium phosphate buffer (0.1 M; pH = 7.2) forming a lightly colored beige/pink solution. Unlike NiSOD, which is isolated as a 1:1 mixture of oxidized (Ni(III)) and reduced (Ni(II)) forms, [Ni(SOD(M1))] can only be isolated in the Ni(II) oxidation state. The UV/vis, X-ray absorption, and CD spectra of [Ni(II)(SOD(M1))] correspond well with those reported for the reduced form of NiSOD. Despite the fact that [Ni(III)(SOD(M1))] is not isolable, [Ni(SOD(M1))] has an appropriate redox potential to act as an SOD (E(1/2) = 0.70(2) V vs Ag/AgCl) and in fact will catalytically disproportionate >40 000 equiv of KO(2).