Mixed activation and mixed inhibition of the oxidoreductase activity of Rhus vernicifera laccase by different Pd~(2 ) ion concentration

Kinetic experiments were performed to study the effects of Pd²⁺ ion on the oxidation of 5,6-dibromo-2, 3-dicyanohydroquinone catalyzed by Rhus vernicifera laccase under condition of pH 4.5 and 30 ± 0.1°C. The results showed that the mixed activation could be observed when Pd² ion was at low concentrations. The competitive and non-competitive activation constants were 9 × 10^?-⁶ and 2 × 10^?-⁶ mol/L, respectively. With the increase of Pd²⁺ ion concentration, the activation was gradually converted into mixed inhibition, and the competitive and non-competitive inhibition constants were 6 × 10^?-⁶ and 32 × 10^?-⁶ mol/L, respectively.