Superoxide dismutases enzymatic assays

In order to monitor SOD activity routinely, assays that require only instrumentation typical of a chemical or biochemical laboratory were set up. The assays consist of a reaction mixture that generates superoxide anion and a coupled redox reaction that scavenges the superoxide ion. The latter reaction is usually followed spectrophoto-metrically. The addition of superoxide dismutase destroys superoxide and inhibits the coupled reaction. The specific activity of the enzyme is determined on the basis of the amount of protein required to slow down to 50% the first-order coupled reaction, i.e., one enzymatic unit is the amount of protein that reduces the rate to 50% and the specific activity corresponds to the number of units per milligram of protein. 

Three decades elapsed between the first isolation of erythrocuprein and the discovery of a catalytic function for this protein. Attributable to the high interest in the biochemistry of reactive oxygen species, numerous enzymatic assays for superoxide dismutases were developed in the last years. Nevertheless, the original assay of McCord and Fridovich is still currently used for routine purposes The reactivity of super-... 

In general, all these indirect assays are well suited for qualitative or half quantitative measurements. Exact evaluations of the enzymatic activities of superoxide dismutases are better performed using direct assays, though, sometimes erroneous conclusions are possible. The strong point of the latter assays is, that velocity constants and reaction orders can be easily determined. 

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