title: Bicarbonate enhances the peroxidase activity of Cu,Zn-superoxide dismutase. Role of carbonate anion radical.
abstract: We examined the effect of bicarbonate on the peroxidase activity of copper-zinc superoxide dismutase (SOD1), using the nitrite anion as a peroxidase probe. Oxidation of nitrite by the enzyme-bound oxidant results in the formation of the nitrogen dioxide radical, which was measured by monitoring 5-nitro-gamma-tocopherol formation. Results indicate that the presence of bicarbonate is not required for the peroxidase activity of SOD1, as monitored by the SOD1/H(2)O(2)-mediated nitration of gamma-tocopherol in the presence of nitrite. However, bicarbonate enhanced SOD1/H(2)O(2)-dependent oxidation of tocopherols in the presence and absence of nitrite and dramatically enhanced SOD1/H(2)O(2)-mediated oxidation of unsaturated lipid in the presence of nitrite. These results, coupled with the finding that bicarbonate protects against inactivation of SOD1 by H(2)O(2), suggest that SOD1/H(2)O(2) oxidizes the bicarbonate anion to the carbonate radical anion. Thus, the amplification of peroxidase activity of SOD1/H(2)O(2) by bicarbonate is attributed to the intermediary role of the diffusible oxidant, the carbonate radical anion. We conclude that, contrary to a previous report (Sankarapandi, S., and Zweier, J. L. (1999) J. Biol. Chem. 274, 1226-1232), bicarbonate is not required for peroxidase activity mediated by SOD1 and H(2)O(2). However, bicarbonate enhanced the peroxidase activity of SOD1 via formation of a putative carbonate radical anion. Biological implications of the carbonate radical anion in free radical biology are discussed.
authors.affiliation: Biophysics Research Institute, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA.
authors.forename: S P
authors.initials: SP
authors.lastname: Goss
authors.forename: R J
authors.initials: RJ
authors.lastname: Singh
authors.forename: B
authors.initials: B
authors.lastname: Kalyanaraman
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D004578:Electron Spin Resonance Spectroscopy; D004789:Enzyme Activation; D005609:Free Radicals; D007700:Kinetics; D010544:Peroxidases / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism*; D014810:Vitamin E / Q000494:pharmacology
chemical_list: D001639:Bicarbonates; D005609:Free Radicals; D014810:Vitamin E; D010544:Peroxidases; D013482:Superoxide Dismutase