Influence of temperature, pH and metal ions on guaiacol oxidation of purified laccase from Leptographium qinlingensis.

The bark beetle Dendroctonus armandi is able to kill living Pinus armandi and has caused serious damage to pine forest in Northern China. As the most important symbiotic fungus of D. armandi, Leptographium qinlingensis plays an important role in the invasion process of the bark beetle. The laccase secreted by it are involved in lignin degradation to provide utilizable nutrition for D. armandi, and catalyze some biochemical reactions, causing the damages of tree tissue. In present study, the extracellular laccase of L. qinlingensis was purified by using the ammonium sulfate precipitation and DEAE-cellulose (DE-52) column chromatography. Furthermore, the effects of temperature, pH value and metal ions on it were investigated and characterized. The purified enzyme exerted its optimal activity with guaiacol. The catalytic efficiencies K(m) and V(max) determined for substrate guaiacol were 15.4 μM and 372.9 IU mg⁻¹, respectively. The optimum pH and temperature for the purified enzyme was 4.4 and 45 °C, respectively, with the highest enzyme specific activity of 7,000 IU mg⁻¹. Moreover, the metal ions, Co²⁺, Mn²⁺, Ca²⁺, Mg²⁺, Fe²⁺ and Cd²⁺, especially Hg²⁺, showed significantly inhibition effects on its activity. To understand the characteristics of this laccase might provide an opportunity and theoretical basis to promote integrated pest management of D. armandi.