title: Multi-frequency e.p.r. studies of a mercury-containing mixed-metal derivative of laccase.
abstract: Multi-frequency e.p.r. studies of a derivative of laccase containing one mercury atom and three of copper were carried out at -150 degrees C. The e.p.r. signal of the mercury derivative and fluoride-binding studies establish that a type-2-like copper centre is present. The signal suffers broadening, owing to g-strain, but at low frequencies (S-band) ligand hyperfine splitting can be resolved, and it can be explained in terms of coupling to three nitrogen atoms. The g values and the effect of solvent deuteration on the line width suggest that the fourth ligand in the equatorial plane is a water molecule. Simulations of the e.p.r. spectrum reveal that the site is slightly rhombic at -150 degrees C, a finding in accord with the proposed N3O donor set. Finally, it is emphasized that a structural reorganization of the type-2 copper site occurs with the binding of fluoride at low temperature. The reorganization may be linked to a conformational change which has previously been claimed to occur on cooling; however, this transition is not necessarily relevant to the temperature-dependence of fluoride binding.
mesh_terms: D001665:Binding Sites; D003300:Copper / Q000032:analysis; D004578:Electron Spin Resonance Spectroscopy; D005459:Fluorides / Q000378:metabolism; D042845:Laccase; D008628:Mercury / Q000032:analysis*; D010088:Oxidoreductases; D013696:Temperature
chemical_list: D003300:Copper; D010088:Oxidoreductases; D042845:Laccase; D008628:Mercury; D005459:Fluorides