Catalytic activity of superoxide dismutase : A method based on its concentration-dependent constant decrease in rate of autoxidation of pyrogallol

A blue copper protein was isolated in 1938 by Mann and $Keilin^1$ from erythrocytes and liver and later from many animal tissues, prompting the names hemocuprein, erythrocuprein, cerebrocuprein and cytocuprein. Discovery of its catalytic activity of dismutating two molecules of superoxide $(O^-_2^\bullet)$ to $H_2O_2 + O_2$ in 1969 by McCord and $Fridovich^2$, led to the rechristening this protein as superoxide dismutase (SOD). Since then it became iconic in studies on oxygen radicals and their toxicity. Inhibition by SOD protein, of the reduction of cytochrome $c$ by superoxide generated by xanthine oxidase reaction remains the best method of its $assay^2.$ Indeed inhibition by this protein of a reaction is equated to the presence and participation of superoxide, sometimes resorting to chain $amplification^3$ of presumed traces.