Reactive oxygen species (ROS) are a major factor in the development of several types of cancer, inflammation, and related diseases. These ROS are not only cytotoxic but also involved in cell signaling. [1] The protection from ROS is of vital importance for biological organisms. For aerobic organisms, superoxide dismutases (SODs) play the major role in protecting cells from ROS, which are generated by the reduction of molecular oxygen by reactive metabolites of the respiratory chain. Because of their biological and medical importance, SODs are a subject of intense research, which yielded more than 2000 publications in the first six months of 2010. While this research has led to detailed knowledge about their biological function and enzyme kinetics, the precise mode of action of these enzymes is still not known and two different mechanisms were proposed. [3] A major reason for this lack of knowledge is the high catalytic rate constants of superoxide degradation (O 2 C À ) by SODs. SODs destroy the superoxide anion radical by converting it into hydrogen peroxide and oxygen with a rate near the diffusion limit (k cat > 2 10 9 m À1 s À1 ). [4] Thus all transients involved in their action are too short lived to be amenable for a spectroscopic characterization. For this reason model systems of SODs were developed. Herein we show that the investigation of a model