Mechanism of the peroxidase activity of Cu, Zn superoxide dismutase

Abstract

In addition to its very efficient catalysis of the dismutation of superoxide ( O 2 - ) into O 2 plus H 2O 2, Cu, Zn SOD acts less efficiently as a non-specific peroxidase. This peroxidase activity is CO 2 dependent although very slow peroxidation of some substrates occurs in the absence of CO2. The mechanism of that CO 2 dependence is explained by the generation of a strong oxidant at the copper site by two sequential reactions with H 2O 2, followed by the oxidation of CO 2 to the carbonate radical that then diffuses into the bulk solution. This diffusible carbonate radical is then responsible for the diverse oxidations that have been reported. A different mechanism that involves the reduction of peroxymonocarbonate by the reduced superoxide dismutase to yield carbonate radical has been proposed. We will demonstrate that this mechanism is not supported by the available data. It seems likely that generation of the carbonate radical has relevance to the oxidative stress faced by aerobic organisms.