title: Thermodynamic and EPR characteristics of a HiPIP-type iron-sulfur center in the succinate dehydrogenase of the respiratory chain.
abstract: In addition to the two species of ferredoxin-type iron-sulfur centers (Centers S-1 and S-2), a third iron-sulfur center (Center S-3), which is paramagnetic in the oxidezed state analogous to the bacterial high potential iron-sulfur protein, has bwen detected in the reconstitutively active soluble succinate dehydrogenase preparation. Midpoint potential (at pH 7.4) of Center S-3 determined in a particulate succinate-cytochrome c reductase is +60 +/- 15 mV. In soluble form, Center S-3 becomes extremely labile towards oxygen or ferricyanide plus phenazine methosulfate similar to reconstitutive activity of the dehydrogenase. Thus, even freshly prepared reconstitutively active enzyme preparations show EPR spectra of Center S-3 which correspond approximately to 0.5 eq per flavin; in particulate preparations this component was found in a 1:1 ratio to flavin. All reconstitutively inactive dehydrogenase preparations that Center S-3 is an innate constituent of succinate dehydrogenase and plays an important role in mediating electrons from the flavoprotein subunit to most probably ubiquinone and then to the cytochrome chain.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy; D005292:Ferricyanides; D007501:Iron / Q000032:analysis; D007700:Kinetics; D008931:Mitochondria, Muscle / Q000201:enzymology; D009206:Myocardium; D010084:Oxidation-Reduction; D011485:Protein Binding; D011487:Protein Conformation; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013455:Sulfur / Q000032:analysis; D013816:Thermodynamics
chemical_list: D005292:Ferricyanides; D013455:Sulfur; D007501:Iron; D013385:Succinate Dehydrogenase