Copper, zinc superoxide dismutase and H2O2. Effects of bicarbonate on inactivation and oxidations of NADPH and urate, and on consumption of H2O2.
Copper,zinc superoxide dismutase (Cu,Zn-SOD) catalyzes the HCO(3)(-)-dependent oxidation of diverse substrates. The mechanism of these oxidations involves the generation of a strong oxidant, derived from H(2)O(2), at the active site copper. This bound oxidant then oxidizes HCO(3)(-) to a strong and diffusible oxidant, presumably the carbonate anion radical that leaves the active site and then oxidizes the diverse substrates. Cu,Zn-SOD is also subject to inactivation by H(2)O(2). It is now demonstrated that the rates of HCO(3)(-)-dependent oxidations of NADPH and urate exceed the rate of inactivation of the enzyme by approximately 100-fold. Cu,Zn-SOD is also seen to catalyze a HCO(3)(-)-dependent consumption of the H(2)O(2) and that HCO(3)(-) does not protect Cu,Zn-SOD against inactivation by H(2)O(2). A scheme of reactions is offered in explanation of these observations.
Liochev
Stefan I
SI
Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
Fridovich
Irwin
I
D001639:Bicarbonates / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism*; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D013482:Superoxide Dismutase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014527:Uric Acid / Q000378:metabolism*
D001639:Bicarbonates; D014527:Uric Acid; D009249:NADP; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase