title: Redox activation of mitochondrial intermembrane space Cu,Zn-superoxide dismutase.
abstract: The localization of Cu,Zn-superoxide dismutase in the mitochondrial intermembrane space suggests a functional relationship with superoxide anion (O2*-) released into this compartment. The present study was aimed at examining the functionality of Cu,Zn-superoxide dismutase and elucidating the molecular basis for its activation in the intermembrane space. Intact rat liver mitochondria neither scavenged nor dismutated externally generated O2*-, unless the mitochondrial outer membrane was disrupted selectively by digitonin. The activation of the intermembrane space Cu,Zn-superoxide dismutase following the disruption of mitochondrial outer membrane was largely inhibited by bacitracin, an inhibitor of protein disulphide-isomerase. Thiol alkylating agents, such as N-methylmaleimide or iodoacetamide, decreased intermembrane space Cu,Zn-superoxide dismutase activation during, but not after, disruption of the outer membrane. This inhibitory effect was overcome by exposing mitochondria to low micromolar concentrations of H2O2 before disruption of the outer membrane in the presence of the alkylating agents. Moreover, H2O2 treatment alone enabled intact mitochondria to scavenge externally generated O2*-. These findings suggest that intermembrane space Cu,Zn-superoxide dismutase is inactive in intact mitochondria and that an oxidative modification of its critical thiol groups is necessary for its activation.
authors.affiliation: Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Universidad de Zaragoza. 50009-Zaragoza, Spain.
authors.forename: Pedro
authors.initials: P
authors.lastname: Iñarrea
authors.forename: Hadi
authors.initials: H
authors.lastname: Moini
authors.forename: Daniel
authors.initials: D
authors.lastname: Rettori
authors.forename: Derick
authors.initials: D
authors.lastname: Han
authors.forename: Jesús
authors.initials: J
authors.lastname: Martínez
authors.forename: Inés
authors.initials: I
authors.lastname: García
authors.forename: Erika
authors.initials: E
authors.lastname: Fernández-Vizarra
authors.forename: María
authors.initials: M
authors.lastname: Iturralde
authors.forename: Enrique
authors.initials: E
authors.lastname: Cadenas
mesh_terms: D000818:Animals; D004789:Enzyme Activation / Q000502:physiology*; D006861:Hydrogen Peroxide / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D008930:Mitochondria, Liver / Q000201:enzymology* / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000378:metabolism; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar; D013438:Sulfhydryl Compounds / Q000502:physiology; D013482:Superoxide Dismutase / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D013438:Sulfhydryl Compounds; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase