Q-band Electron Nuclear Double Resonance Research Articles

95/00288 Monopoly issue emerges as political bombshell

The g-tensor of excess electron centres (H+)(e−) generated at the surface of polycrystalline MgO has been determined by multi-frequency, high-field electron-paramagnetic resonance (EPR) performed at 9.5, 34, 190 and 285 GHz. The A tensor for the interacting 1H was also determined by complementary Q-band electron-nuclear double resonance (ENDOR). Due to the high spectral resolution the anisotropy of the g-tensor could be fully resolved in the powder continuous-wave EPR spectrum. Computer simulation of the experimental data revealed small g-tensor anisotropies: Δgx = −0.00294, Δgy = −0.00286, Δgz = −0.00101, with Δgi = gi − 2.0023.

Q-band ENDOR spectra of the Rieske protein from Rhodobactor capsulatus ubiquinol-cytochrome c oxidoreductase show two histidines coordinated to the [2Fe-2S] cluster.

Electron nuclear double resonance (ENDOR) experiments were performed on 14N (natural abundance) and 15N-enriched iron-sulfur Rieske protein in the ubiquinol-cytochrome c2 oxidoreductase from Rhodobactor capsulatus. The experiments proved that two distinct nitrogenous ligands, histidines, are undoubtedly ligated to the Rieske [2Fe-2S] center. The calculations of hyperfine tensors give values similar but not identical to those of the Rieske-type cluster in phthalate dioxygenase of Pseudomonas cepacia and suggest a slightly different geometry of the iron-sulfur cluster in the two proteins.