title: Paramagnetic properties of the halide-bound derivatives of oxidised tyrosinase investigated by 1H NMR spectroscopy.
abstract: The (1)H NMR relaxation characteristics of the histidines in the oxidised type-3 copper site of tyrosinase (Ty(met)) from the bacterium Streptomyces antibioticus in the halide-bound forms (Ty(met)X with X = F(-), Cl(-), Br(-)) have been determined and analysed. The (1)H NMR spectra of the Ty(met)X species display remarkably sharp, well-resolved, paramagnetically shifted (1)H signals, which originate from the protons of the six His residues coordinated to the two Cu(II) ions in the type-3 centre. From the temperature-dependence of the (1)H paramagnetic shifts the following values for the exchange-coupling parameter -2J were determined: 260 (Ty(met)F), 200 (Ty(met)Cl) and 162 cm(-1) (Ty(met)Br). The (1)H T(1) relaxation is dipolar in origin and correlates with the Cu--H distances. Electronic relaxation times tau(S) derived from the (1)H T(1) data amount to about 10(-11) s and follow the order Ty(met)F>Ty(met)Cl>Ty(met)Br. They are two orders of magnitude shorter than the tau(S) values reported for mononuclear copper systems, in accordance with the sharpness of the (1)H signals. The results corroborate the Cu(2) bridging mode of the halide ions. On the basis of the measured hyperfine interaction constants for the ligand histidine nuclei, it is concluded that 70-80 % of the spin density in the excited triplet state resides on the two copper ions and the bridging atoms.
authors.affiliation: Leiden Institute of Chemistry Gorlaeus Laboratories, Leiden University Einsteinweg 55, 2333 CC, Leiden, The Netherlands.
authors.forename: Armand W J W
authors.initials: AW
authors.lastname: Tepper
authors.forename: Luigi
authors.initials: L
authors.lastname: Bubacco
authors.forename: Gerard W
authors.initials: GW
authors.lastname: Canters
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D003300:Copper; D006219:Halogens / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008280:Magnetics; D014442:Monophenol Monooxygenase / Q000737:chemistry*; D013303:Streptomyces antibioticus / Q000201:enzymology*; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D006219:Halogens; D006639:Histidine; D003300:Copper; D014442:Monophenol Monooxygenase