A study of the pH dependence of the activity of porcine Cu,Zn superoxide dismutase

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Abstract

The enzyme activity of porcine Cu,Zn superoxide dismutase, which has an unusually high isoelectric point, decreases almost linearly with increasing pH between pH 7.5 and 12.0, while EPR and NMR parameters of the copper are titrated only above pH 9.5. Elimination of lysine charges by succinylation abolishes the pH dependence of activity between pH 7.5 and 9.5 and produces identical pH-activity curves for both bovine and porcine enzymes. The pH dependence of activity of the succinylated proteins overlaps that of the spectroscopic parameters of the copper in both enzymes. These results indicate that lysines play a critical role in the rate determining step of the mechanism of the Cu,Zn superoxide dismutases.

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