title: Autoxidation of Reduced Horse Heart Cytochrome c Catalyzed by Cardiolipin-Containing Membranes.
abstract: Visible circular dichroism, absorption, and fluorescence spectroscopy were used to probe the binding of horse heart ferrocytochrome c to anionic cardiolipin (CL) head groups on the surface of 1,1',2,2'-tetraoleoyl cardiolipin (TOCL)/1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) (20%:80%) liposomes in an aerobic environment. We found that ferrocytochrome c undergoes a conformational transition upon binding that leads to complete oxidation of the protein at intermediate and high CL concentrations. At low lipid concentrations, the protein maintains a structure that is only slightly different from its native one, whereas an ensemble of misligated predominantly hexacoordinated low-spin states become increasingly populated at high lipid concentrations. A minor fraction of conformations with either high- or quantum-mixed-spin states were detected at a CL to protein ratio of 200 (the largest one investigated). The population of the non-native state is less pronounced than that found for cytochrome c-CL interactions initiated with oxidized cytochrome c. Under anaerobic conditions, the protein maintains its reduced state but still undergoes some conformational change upon binding to CL head groups on the liposome surface. Our data suggest that CL-containing liposomes function as catalysts by reducing the activation barrier for a Fe2+→ O2electron transfer. Adding NaCl to the existing cytochrome-liposome mixtures under aerobic conditions inhibits protein autoxidation of ferrocytochrome c and stabilizes the reduced state of the membrane-bound protein.
authors.affiliation: Department of Chemistry, Drexel University , 3141 Chestnut Street, Philadelphia, Pennsylvania 19104, United States.
authors.forename: Lee
authors.initials: L
authors.lastname: Serpas
authors.affiliation: Department of Chemistry, Drexel University , 3141 Chestnut Street, Philadelphia, Pennsylvania 19104, United States.
authors.forename: Bridget
authors.initials: B
authors.lastname: Milorey
authors.affiliation: Department of Chemistry, Drexel University , 3141 Chestnut Street, Philadelphia, Pennsylvania 19104, United States.
authors.forename: Leah A
authors.initials: LA
authors.lastname: Pandiscia
authors.affiliation: Department of Chemistry, Drexel University , 3141 Chestnut Street, Philadelphia, Pennsylvania 19104, United States.
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Addison
authors.affiliation: Department of Chemistry, Drexel University , 3141 Chestnut Street, Philadelphia, Pennsylvania 19104, United States.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Schweitzer-Stenner
mesh_terms: D000818:Animals; D055162:Biocatalysis; D002308:Cardiolipins / Q000737:chemistry / Q000378:metabolism*; D045304:Cytochromes c / Q000737:chemistry / Q000378:metabolism*; D006321:Heart; D006736:Horses; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction
chemical_list: D002308:Cardiolipins; D008081:Liposomes; D045304:Cytochromes c