title: The use of high field/frequency EPR in studies of radical and metal sites in proteins and small inorganic models.
abstract: Low temperature electron paramagnetic resonance (EPR) spectroscopy with frequencies between 95 and 345 GHz and magnetic fields up to 12 T have been used to study radicals and metal sites in proteins and small inorganic model complexes. We have studied radicals, Fe, Cu and Mn containing proteins. For S = 1/2 systems, the high frequency method can resolve the g-value anisotropy. It was used in mouse ribonucleotide reductase (RNR) to show the presence of a hydrogen bond to the tyrosyl radical oxygen. At 285 GHz the type 2 Cu(II) signal in the complex enzyme laccase is clearly resolved from the Hg(II) containing laccase peroxide adduct. For simple metal sites, the systems over S = 1/2 can be described by the spin Hamiltonian: H(S) = BgS + D[Sz2 - S(S + 1)/3 + E/D (Sx2 - Sy2)]. From the high frequency EPR the D-value can be determined directly by, (I) shifts of g(eff) for half-integer spin systems with large D-values as observed at 345 GHz on an Fe(II)-NO-EDTA complex, which is best described as S = 3/2 system with D = 11.5 cm(-1), E = 0.1 cm(-1) and gx = gy = gz = 2.0; (II) measuring the outermost signal, for systems with small D values, distant of (2S - 1) x absolute value(D) from the center of the spectrum as observed in S= 5/2 Fe(III)-EDTA. In Mn(II) substituted mouse RNR R2 protein the weakly interacting Mn(II) at X-band could be observed as decoupled Mn(II) at 285 GHz.
authors: Department of Biochemistry, University of Oslo, Blindern, Norway. k.k.andersson@biokjemi.uio.no
authors: K Kristoffer
authors: KK
authors: Andersson
authors: Anne-Laure
authors: AL
authors: Barra
mesh_terms: D000818:Animals; D016880:Anisotropy; D055592:Biophysical Phenomena; D001703:Biophysics; D003300:Copper / Q000032:analysis; D004574:Electromagnetic Fields; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005609:Free Radicals; D006860:Hydrogen Bonding; D007501:Iron / Q000032:analysis; D042845:Laccase; D008345:Manganese / Q000032:analysis; D008670:Metals / Q000032:analysis*; D051379:Mice; D010088:Oxidoreductases / Q000737:chemistry; D011506:Proteins / Q000032:analysis; D012264:Ribonucleotide Reductases / Q000032:analysis
chemical_list: D005609:Free Radicals; D008670:Metals; D011506:Proteins; D008345:Manganese; D003300:Copper; D007501:Iron; D010088:Oxidoreductases; D042845:Laccase; D012264:Ribonucleotide Reductases