Reaction of Copper-Zinc Superoxide Dismutase with Hydrogen Peroxide:  A Possible Source of Heterogeneity

ABSTRACT (condensed)

The reaction of hydrogen peroxide with copper-zinc bovine superoxide dismutase at ratios of 0.2 to 4.0 per active site at pH 10.0 results in the formation of distinct electrophoretic forms of the enzyme.  The mobilities of these forms are identical to the mobilities of the forms present in heterogeneous, untreated native samples in two different electrophoretic systems, pH 6.96 (TRIS-acetic acid) and pH 8.38 (TRIS-glycine).  Analysis of several purified preparations of superoxide dismutase have indicated that a lower copper content is correlated with an increased heterogeneity.  For all samples, this heterogeneity was not altered by the addition of copper and zinc.  In view of these observations we would like to suggest that the reaction with hydrogen peroxide in vivo may be the source of the heterogeneity so often seen in purified preparations of the copper-zinc enzyme.   Hydrogen peroxide is the product of the enzyme-catalyzed dismutation reaction of superoxide anion and its reaction with the dismutase, though slow, could lead to the accumulation of altered proteins that copurify with the native enzyme in classical isolation procedures.