Temperature dependence of the reduction potential of blue copper in fungal laccase.

Thin-layer spectroelectrochemical methods have been employed to measure the reduction potentials of the blue copper in Polyporus versicolor laccase (EC 1.10.3.2) between 7 degrees C and 41 degrees C (0.2 M sodium phosphate, pH 5.4). Thermodynamic parameters are: DeltaS degrees = -13.9 +/- 2 cal/mol-K; DeltaH degrees = -22.1 +/- 0.5 kcal/mol; E degrees (25 degrees C) = 780 +/- 3 mV vs. the normal hydrogen electrode. Comparison of the DeltaS degrees and DeltaH degrees values with those for single-site proteins suggests that the high potential of the blue copper in fungal laccase is attributable mainly to stabilization of the copper (I) center by enhanced ligand binding interactions and that protein solvation effects play a lesser role.