Abstract
The effect of bicarbonate anion (HCO(3)(-)) on the peroxidase activity of copper, zinc superoxide dismutase (SOD1) was investigated using three structurally different probes: 5, 5'-dimethyl-1-pyrroline N-oxide (DMPO), tyrosine, and 2, 2'-azino-bis-[3-ethylbenzothiazoline]-6-sulfonic acid (ABTS). Results indicate that HCO(3)(-) enhanced SOD/H(2)O(2)-dependent (i) hydroxylation of DMPO to DMPO-OH as measured by electron spin resonance, (ii) oxidation and nitration of tyrosine to dityrosine, nitrotyrosine, and nitrodityrosine as measured by high pressure liquid chromatography, and (iii) oxidation of ABTS to the ABTS cation radical as measured by UV-visible spectroscopy. Using oxygen-17-labeled water, it was determined that the oxygen atom present in the DMPO-OH adduct originated from H(2)O and not from H(2)O(2). This result proves that neither free hydroxyl radical nor enzyme-bound hydroxyl radical was involved in the hydroxylation of DMPO. We postulate that HCO(3)(-) enhances SOD1 peroxidase activity via formation of a putative carbonate radical anion. This new and different perspective on HCO(3)(-)-mediated oxidative reactions of SOD1 may help us understand the free radical mechanism of SOD1 and related mutants linked to amyotrophic lateral sclerosis.
Highlights
Bicarbonate anion (HCO3Ϫ) is abundantly present in biological systems [1]
We show that HCO3Ϫ enhances (i) the hydroxylation of nitrone spin trap, dimethyl-1-pyrroline N-oxide (DMPO), (ii) oxidation and nitration of tyrosine, and (iii) oxidation of the peroxidase probe ABTS to the ABTS radical cation in the presence of SOD1 and H2O2
We propose that the carbonate anion radical (CO3.) formed from oxidation of HCO3Ϫ at the active site of SOD1 by the copper, zinc SOD-bound hydroxyl radical (SOD1-Cu2ϩ-1⁄7OH) is responsible for hydroxylation of DMPO, oxidation and nitration of tyrosine, and oxidation of ABTS
Summary
Received for publication, December 21, 1999, and in revised form, February 17, 2000. Hao Zhang, Joy Joseph, Christopher Felix, and B. We postulate that HCO3Ϫ enhances SOD1 peroxidase activity via formation of a putative carbonate radical anion This new and different perspective on HCO3Ϫ-mediated oxidative reactions of SOD1 may help us understand the free radical mechanism of SOD1 and related mutants linked to amyotrophic lateral sclerosis. We show that HCO3Ϫ enhances (i) the hydroxylation of nitrone spin trap, DMPO, (ii) oxidation and nitration of tyrosine, and (iii) oxidation of the peroxidase probe ABTS to the ABTS radical cation in the presence of SOD1 and H2O2. We propose that the carbonate anion radical (CO3.) formed from oxidation of HCO3Ϫ at the active site of SOD1 by the copper, zinc SOD-bound hydroxyl radical (SOD1-Cu2ϩ-1⁄7OH) is responsible for hydroxylation of DMPO, oxidation and nitration of tyrosine, and oxidation of ABTS. The proposed mechanism offers a new and different perspective on the peroxidative reactions catalyzed by the enzyme SOD1
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
