Mechanism of hydrogen peroxide-induced Cu,Zn-superoxide dismutase-centered radical formation as explored by immuno-spin trapping: the role of copper- and carbonate radical anion-mediated oxidations.

RAMIREZ, DC; GOMEZ MEJIBA, SE; MASON, RP

FREE RADICAL BIOLOGY AND MEDICINE

ELSEVIER SCIENCE INC

Lugar: Amsterdam; Año: 2005 vol. 38 p. 201 - 214

0891-5849

Free Radic Biol Med. 2005 Jan 15;38(2):201-14. Mechanism of hydrogen peroxide-induced Cu,Zn-superoxide dismutase-centered radical formation as explored by immuno-spin trapping: the role of copper- and carbonate radical anion-mediated oxidations. Ramirez DC1, Gomez Mejiba SE, Mason RP. Author information 1Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health, 111 T.W. Alexander Drive, Research Triangle Park, NC 27709, USA. ramirez1@niehs.nih.gov Abstract We have reinvestigated the biochemistry of H2O2-induced Cu,Zn-superoxide dismutase (SOD1)-centered radicals, detecting them by immuno-spin trapping. These radicals are involved in H2O2-induced structural and functional damage to SOD1, and their mechanism of generation depends on copper and/or (bi)carbonate (i.e., CO2, CO3(-2), or HCO3-). First, in the absence of DTPA and (bi)carbonate, Cu(II) was partially released and rebound at His, Cys, and Tyr residues in SOD1 with the generation of protein-copper-bound oxidants outside the SOD1 active site by reaction with excess H2O2. These species produced immuno-spin trapping-detectable SOD1-centered radicals associated with H2O2-induced active site ( approximately 5 and approximately 10 kDa fragments) and non-active site (smearing between 3 and 16 kDa) copper-dependent backbone oxidations and subsequent fragmentation of SOD1. Second, in the presence of DTPA, which inhibits H2O2-induced SOD1 non-active site fragmentation, (bi)carbonate scavenged the enzyme-bound oxidant at the SOD1 active site to produce the carbonate radical anion, CO3*-, thus protecting against active site SOD1 fragmentation. CO3*- diffuses and produces side chain oxidations forming DMPO-trappable radical sites outside the enzyme active site. Both mechanisms for generating immuno-spin trapping-detectable SOD1-centered radicals were susceptible to inhibition by cyanide and enhanced at high pH values. In addition, (bi)carbonate enhanced H2O2-induced SOD1 turnover as demonstrated by an enhancement in oxygen evolution and SOD1 inactivation. These results help clarify the free radical chemistry involved in the functional and structural oxidative damage to SOD1 by H2O2 with the intermediacy of copper- and CO3*--mediated oxidations.