title: Mössbauer study of the inactive Fe3S4 and Fe3Se4 and the active Fe4Se4 forms of beef heart aconitase.
abstract: Active beef heart aconitase contains an iron-sulfur cluster with an [Fe4S4]2+ core. This cluster can be converted into Fe3S4 with concomitant loss of enzymatic activity. We have reconstituted apo-aconitase with iron and selenide to obtain Fe4Se4 aconitase. The Se analog has higher catalytic activity than the native S-containing enzyme when isocitrate is the substrate. Oxidation of [Fe4Se4]2+ with ferricyanide yields the inactive [Fe3Se4]1+ form. The Se-containing 3-Fe cluster can be reduced to [Fe3Se4]0. We have studied the [Fe3S4]1+,0, [Fe3Se4]1+,0, and [Fe4Se4]2+ states with Mössbauer spectroscopy from 1.3 K to 200 K in magnetic fields up to 6.0 T. The spectra of the S- and Se-containing enzymes were found to be remarkably similar. The spectra of the 3-Fe clusters were analyzed and the salient features of the electronic structure are discussed.
authors.affiliation: Gray Freshwater Biological Institute, University of Minnesota, Navarre 55392.
authors.forename: K K
authors.initials: KK
authors.lastname: Surerus
authors.forename: M C
authors.initials: MC
authors.lastname: Kennedy
authors.forename: H
authors.initials: H
authors.lastname: Beinert
authors.forename: E
authors.initials: E
authors.lastname: Münck
mesh_terms: D000154:Aconitate Hydratase / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D007501:Iron / Q000032:analysis*; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D007700:Kinetics; D008667:Metalloproteins / Q000378:metabolism*; D009206:Myocardium / Q000201:enzymology; D010084:Oxidation-Reduction; D013057:Spectrum Analysis / Q000379:methods; D013455:Sulfur / Q000032:analysis*
chemical_list: D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D013455:Sulfur; D007501:Iron; D000154:Aconitate Hydratase