A Mechanistic Study of the Copper(II)-Peptide-Cataly zed Superoxide Dismutation. A Pulse Radiolysis Study

The reactivity of O₂^- toward Cu(II)-peptides containing glycine and histidine for which E°cu(III)/Cu(II) ≤ 108 V was investigated by the pulse radiolysis technique. It has been found that the ability of the various complexes to catalyze O₂^- dismutation depends inversely on the redox potential of the couple Cu(III)/Cu(II). The Cu(II)-peptides containing histidine, which have higher redox potentials than that of the couple O₂^-/H₂O₂, do not catalyze the reaction at all. Although no direct evidence was found for the formation of Cu(III)-peptide, the results suggest that the mechanism of the catalysis of Of dismutation proceeds via alternate oxidation and reduction of the metal by O₂^-. Furthermore, this mechanism is supported by indirect observations, which are discussed in detail.