title: Interaction of 9,10-phenanthraquinone with dithiol causes oxidative modification of Cu,Zn-superoxide dismutase (SOD) through redox cycling.
abstract: 9,10-Phenanthraquinone (9,10-PQ) is abundant in diesel exhaust particles (DEP) and causes oxidative protein modification in cells. We previously reported that redox cycling of 9,10-PQ with dithiols leads to the generation of an excess of superoxide (O₂•⁻). Cu,Zn-superoxide dismutase (Cu,Zn-SOD), which dismutates O₂•⁻ to hydrogen peroxide (H₂O₂), is sensitive to its own product, H₂O₂. In this study, incubating 9,10-PQ with dithiols, but not monothiols, for 24 hr, resulted in the conversion of native Cu,Zn-SOD to its charge isomers, some of which did not show enzyme activity. Exposing Cu,Zn-SOD to 9,10-PQ in the presence of dihydrolipoic acid (DHLA), a model for low molecular weight endogenous dithiols, caused a concentration-dependent decrease in the enzyme activity. Under these conditions, copper release from the active site and Cu,Zn-SOD oxidation were detected, the evidence for which was carbonyl formation. Experiments using agents that scavenge reactive oxygen species (ROS) indicated that the hydroxyl radical (•OH) derived from H₂O₂ plays a critical role in the fragmentation of the enzyme. The findings presented suggest that Cu,Zn-SOD readily undergoes oxidative modification associated with activity loss, caused by ROS generated by the redox cycling of 9,10-PQ with endogenous dithiols such as DHLA and, presumably, proximal protein thiols.
authors.affiliation: Master's Program in Environmental Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Japan.
authors.forename: Rie
authors.initials: R
authors.lastname: Koizumi
authors.forename: Keiko
authors.initials: K
authors.lastname: Taguchi
authors.forename: Miwa
authors.initials: M
authors.lastname: Hisamori
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Kumagai
mesh_terms: D020134:Catalytic Domain; D002478:Cells, Cultured; D003300:Copper / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005609:Free Radicals / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D007527:Isoenzymes; D010084:Oxidation-Reduction; D010616:Phenanthrenes / Q000633:toxicity*; D050050:Protein Carbonylation / Q000187:drug effects; D013482:Superoxide Dismutase / Q000378:metabolism* / Q000502:physiology; D008063:Thioctic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000502:physiology; D014050:Toluene / Q000031:analogs & derivatives* / Q000494:pharmacology; D001335:Vehicle Emissions
chemical_list: D005609:Free Radicals; D007527:Isoenzymes; D010616:Phenanthrenes; D001335:Vehicle Emissions; D014050:Toluene; C005399:9,10-phenanthrenequinone; D008063:Thioctic Acid; D003300:Copper; C015144:dihydrolipoic acid; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase; C004848:dithiol