Comparison of malondialdehyde and hydrogen peroxide modified CuZnSOD by EPR spectroscopy

CuZn superoxide dismutase (CuZnSOD) contributes to the regulation of the steady-state concentration of reactive oxygen species in cells and minimizes pathological consequences induced by these reactive oxygen species. During the exaggerated formation of reactive oxygen species, often resulting from an activation of phagocytotic cells, CuZnSOD is administered with a therapeutic purpose. But inhibition of the endogeneous or administered CuZnSOD by products generated during the process of formation of reactive oxygen species (H2O2, HOCl, .OH, products of lipid peroxidation) might intensify cell damage. In this study, we compared the influence of malondialdehyde (MDA, high reactive molecule formed in lipid peroxidation) and H2O2 (known to inhibit the CuZnSOD) on bovine CuZnSOD. MDA reacted with CuZnSOD. The reaction was found to be both time- and concentration-dependent, which was demonstrated by the formation of fluorophors. EPR spectroscopy revealed that this reaction had no influence on the activity of CuZnSOD since the catalytic centre of the CuZnSOD was not effected by MDA. In contrast, H2O2 modified the catalytic centre which caused an activity decrease.