title: ESEEM studies of succinate:ubiquinone reductase from Paracoccus denitrificans.
abstract: Electron spin-echo envelope modulation (ESEEM) spectroscopy has been performed in order to obtain structural information about the environment of the reduced [2Fe-2S] cluster (S-1 center), the oxidized [3Fe-4S] cluster (S-3 center), and the flavin semiquinone radical in purified succinate:ubiquinone reductase from Paracoccus denitrificans. Spectral simulations of the ESEEM data from the reduced [2Fe-2S] yielded nuclear quadrupole interaction parameters that are indicative of peptide nitrogens. We also observed a weak interaction between the oxidized [3Fe-4S] cluster and a peptide 14N. There was no evidence for coordination of any of the Fe atoms to 14N atoms of imidazole rings. The ESEEM data from the flavin semiquinone radical were more complicated. Here, evidence was obtained for interactions between the unpaired electron and only the two nitrogen atoms in the flavin ring.
authors.affiliation: Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena 91125, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: Hung
authors.forename: C V
authors.initials: CV
authors.lastname: Grant
authors.forename: J M
authors.initials: JM
authors.lastname: Peloquin
authors.forename: A R
authors.initials: AR
authors.lastname: Waldeck
authors.forename: R D
authors.initials: RD
authors.lastname: Brit
authors.forename: S I
authors.initials: SI
authors.lastname: Chan
mesh_terms: D000818:Animals; D016227:Benzoquinones / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D004227:Dithionite / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D042963:Electron Transport Complex II; D004926:Escherichia coli / Q000201:enzymology; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism; D005415:Flavins / Q000737:chemistry / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D010231:Paracoccus denitrificans / Q000201:enzymology*; D013385:Succinate Dehydrogenase / Q000737:chemistry* / Q000378:metabolism; D019802:Succinic Acid / Q000378:metabolism
chemical_list: D016227:Benzoquinones; D005415:Flavins; D007506:Iron-Sulfur Proteins; D009097:Multienzyme Complexes; D005182:Flavin-Adenine Dinucleotide; D004227:Dithionite; C025232:semiquinone radicals; D019802:Succinic Acid; D010088:Oxidoreductases; D042963:Electron Transport Complex II; D013385:Succinate Dehydrogenase