title: Relaxation filtered hyperfine (REFINE) spectroscopy: a novel tool for studying overlapping biological electron paramagnetic resonance signals applied to mitochondrial complex I.
abstract: A simple strategy to separate overlapping electron paramagnetic resonance (EPR) signals in biological systems is presented. Pulsed EPR methods (inversion- and saturation-recovery) allow the determination of the T(1) spin-lattice relaxation times of paramagnetic centers. T(1) may vary by several orders of magnitude depending on the species under investigation. These variations can be employed to study selectively individual species from a spectrum that results from an overlap of two species using an inversion-recovery filtered (IRf) pulsed EPR technique. The feasibility of such an IRf field-swept technique is demonstrated on model compounds (alpha,gamma-bisphenylene-beta-phenylallyl-benzolate, BDPA, and 2,2,6,6-tetramethyl-piperidine-1-oxyl, TEMPO) and a simple strategy for the successful analysis of such mixtures is presented. Complex I is a multisubunit membrane protein of the respiratory chain containing several iron-sulfur (FeS) centers, which are observable with EPR spectroscopy. It is not possible to investigate the functionally important FeS cluster N2 separately because this EPR signal always overlaps with the other FeS signals. This cluster can be studied selectively using the IRf field-swept technique and its EPR spectrum is in excellent agreement with previous cw-EPR data from the literature. In addition, the possibility to separate the hyperfine spectra of two spectrally overlapping paramagnetic species is demonstrated by applying this relaxation filter together with hyperfine spectroscopy (REFINE). For the first time, the application of this filter to a three-pulse electron spin-echo envelope modulation (ESEEM) pulse sequence is demonstrated to selectively observe hyperfine spectra on a system containing two paramagnetic species. Finally, REFINE is used to assign the observed nitrogen modulation in complex I to an individual iron-sulfur cluster.
authors.affiliation: Institut für Physikalische und Theoretische Chemie and Zentrum für Biomolekulare Magnetische Resonanz, Johann Wolfgang Goethe-Universität Frankfurt, D-60439 Frankfurt am Main, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Maly
authors.forename: Fraser
authors.initials: F
authors.lastname: MacMillan
authors.forename: Klaus
authors.initials: K
authors.lastname: Zwicker
authors.forename: Noushin
authors.initials: N
authors.lastname: Kashani-Poor
authors.forename: Ulrich
authors.initials: U
authors.lastname: Brandt
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Prisner
mesh_terms: D000498:Allyl Compounds / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry*; D003497:Cyclic N-Oxides / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy / Q000295:instrumentation* / Q000379:methods*; D042967:Electron Transport Complex I / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000737:chemistry; D008956:Models, Chemical; D013113:Spin Labels; D013696:Temperature; D025062:Yarrowia / Q000201:enzymology*
chemical_list: D000498:Allyl Compounds; D001426:Bacterial Proteins; D003497:Cyclic N-Oxides; D007506:Iron-Sulfur Proteins; D013113:Spin Labels; C416323:bis-diphenylene-phenyl-allyl; D042967:Electron Transport Complex I; C003959:TEMPO