Carbonate Anion Radical Generated by the Peroxidase Activity of Copper-Zinc Superoxide Dismutase: Scavenging of Radical and Protection of Enzyme by Hypotaurine and Cysteine Sulfinic Acid

摘要

Copper-zinc superoxide dismutase (SOD) is considered one of the most important mammalian antioxidant defenses and plays a relevant role due to its main function in catalyzing the dismutation of superoxide anion to oxygen and hydrogen peroxide. However, interaction between SOD and H2O2 produced a strong copper--bound oxidant (Cu(II)center dot OH) that seems able to contrast the self-inactivation of the enzyme or oxidize other molecules through its peroxidase activity. The bicarbonate presence enhances the peroxidase activity and produces the carbonate anion radical (CO3 center dot-). CO3 center dot- s a freely diffusible reactive species capable of oxidizing several molecules that are unwieldy to access into the reactive site of the enzyme. Cu(II)center dot OH oxidizes bicarbonate to the CO3 center dot- which spreads out of the binding site and oxidizes hypotaurine and cysteine sulfinic acid to the respective sulfonates through an efficient reaction. These findings suggest a defense role for sulfinates against the damage caused by CO3 center dot- The effect of hypotaurine and cysteine sulfinic acid on the CO3 center dot- mediated oxidation of the peroxidase probe ABTS to ABTS cation radical (ABTS(+)) has been studied. Both sulfinates are able to inhibit the oxidation of ABTS mediated by CO3 center dot- The effect of hypotaurine and