Copper, zinc superoxide dismutase catalyzes hydroxyl radical production from hydrogen peroxide.
Cu,Zn superoxide dismutase (Cu,Zn-SOD; EC 1.15.1.1) is known to be inhibited slowly by H2O2. Using EPR and the spin traps 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) and N-tert-butyl-alpha-phenylnitrone (PBN), we have shown that Cu,Zn-SOD catalyzes the formation of "free" .OH radicals from H2O2 in pH 7.6 bicarbonate buffer. Supporting evidence includes the following: (i) H2O2 and active Cu,Zn-SOD are required to yield significant signals from spin-trap-OH adducts. (ii) With O2-., Cu,Zn-SOD causes the appearance of intense resonance signals due to DMPO-OH adducts. These signals were inhibited strongly by catalase. (iii) With H2O2, Cu,Zn-SOD, and DMPO, radical scavengers formate and azide, but not ethanol, decrease DMPO-OH signals while causing new intense signals due to their corresponding DMPO-radical adducts. Failure of ethanol to quench DMPO-OH signals is discussed in light of the positively charged active channel of the enzyme. (iv) With PBN as a spin trap, ethanol quenches .OH radical signals and yields PBN-trapped hydroxyethyl radical signals. (v) Mn-SOD does not catalyze "free" .OH radical formation and it also exerts no effect on the signals of DMPO-OH adducts when added together with the Cu,Zn-SOD. The capacity of Cu,Zn-SOD to generate "free" .OH radicals from H2O2 may in part explain the biological damage associated with elevated intracellular SOD activity.
Yim
M B
MB
Laboratory of Biochemistry, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892.
Chock
P B
PB
Stadtman
E R
ER
D000818:Animals; D002374:Catalase / Q000378:metabolism; D002417:Cattle; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D004912:Erythrocytes / Q000201:enzymology; D005609:Free Radicals; D006861:Hydrogen Peroxide / Q000378:metabolism*; D006878:Hydroxides / Q000378:metabolism*; D017665:Hydroxyl Radical; D008099:Liver / Q000201:enzymology; D013113:Spin Labels; D013482:Superoxide Dismutase / Q000097:blood*
D003497:Cyclic N-Oxides; D005609:Free Radicals; D006878:Hydroxides; D013113:Spin Labels; D017665:Hydroxyl Radical; C017245:5,5-dimethyl-1-pyrroline-1-oxide; D006861:Hydrogen Peroxide; D002374:Catalase; D013482:Superoxide Dismutase