title: Superoxide radical protects liposome-contained cytochrome c against oxidative damage promoted by peroxynitrite and free radicals.
abstract: The effects of nitrosative species on cyt c structure and peroxidase activity were investigated here in the presence of O(2)(*-) and anionic and zwitterionic vesicles. Nitrosative species were generated by 3-morpholinesydnonymine (SIN1) decomposition, using cyt c heme iron and/or molecular oxygen as electron acceptor. Far- and near-UV CD spectra of SIN1-treated cyt c revealed respectively a slight decrease of alpha-helix content (from 39 to 34%) and changes in the tryptophan structure accompanied by increased fluorescence. The Soret CD spectra displayed a significant decrease of the positive signal at 403 nm. EPR spectra revealed the presence of a low-spin cyt c form (S=1/2) with g(1)=2.736, g(2)=2.465, and g(3)=2.058 after incubation with SIN1. These data suggest that the concomitant presence of NO(*) and O(2)(*-) generated from dissolved oxygen, in a system containing cyt c and liposomes, promotes chemical and conformational modifications in cyt c, resulting in a hypothetical bis-histidine hexacoordinated heme iron. We also show that, paradoxically, O(2)(*-) prevents not only membrane lipoperoxidation by peroxide-derived radicals but also oxidation of cyt c itself due to the ability of O(2)(*-) to reduce heme iron. Finally, lipoperoxidation measurements showed that, although it is a more efficient peroxidase, SIN1-treated cyt c is not more effective than native cyt c in promoting damage to anionic liposomes in the presence of tert-ButylOOH, probably due to loss of affinity with negatively charged lipids.
authors: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil.
authors: Camila M
authors: CM
authors: Mano
authors: Marcelo P
authors: MP
authors: Barros
authors: Priscila A
authors: PA
authors: Faria
authors: Tatiana
authors: T
authors: Prieto
authors: Fábio H
authors: FH
authors: Dyszy
authors: Otaciro R
authors: OR
authors: Nascimento
authors: Iseli L
authors: IL
authors: Nantes
authors: Etelvino J H
authors: EJ
authors: Bechara
mesh_terms: D045304:Cytochromes c / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000737:chemistry / Q000378:metabolism; D015227:Lipid Peroxidation; D015538:Nitrosation; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D009195:Peroxidase / Q000378:metabolism*; D030421:Peroxynitrous Acid / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D017433:Protein Structure, Secondary; D013053:Spectrophotometry; D013481:Superoxides / Q000737:chemistry / Q000378:metabolism; D014364:Tryptophan / Q000737:chemistry; D053835:Unilamellar Liposomes / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D053835:Unilamellar Liposomes; D013481:Superoxides; D030421:Peroxynitrous Acid; D006418:Heme; D014364:Tryptophan; D045304:Cytochromes c; D009195:Peroxidase