Effect of Common Metal Ions and Anions on Laccase Catalysis of Guaiacol and Lignocellulosic Fiber

Abstract

The effects of 12 common metal ionic compounds on the laccase catalytic activity in reactions using guaiacol as the substrate was determined using spectrophotometry. Furthermore, the influence of several metal ionic compounds on the generation of reactive oxygen species (ROS) by oxidation of lignin in jute fiber under laccase catalysis was studied by electron paramagnetic resonance (EPR) spectroscopy using N-tert-butyl-alpha-phenylnitrone (PBN) as the spin-trapping agent. Common metal cations, such as K+, Na+, Mg2+, Ca2+, and Cu2+ and the anion SO42- had almost no effect on laccase activity during the initial stage of the catalytic reactions. High concentrations of the Mn2+ ion exhibited weak inhibition of laccase; Ag+ and NO3- showed a moderate inhibitory effect on laccase activity during the initial stage of the catalytic reactions. Fe2+ had no direct effect on the binding of laccase to its substrate, but strongly retarded the progress of the catalytic reaction by reducing the intermediate free radicals. The ions Cl-, Fe3+, and Ag+ exhibited either strong inhibitory effects on the catalysis of the substrate or a destructive effect on the structure of laccase itself. Furthermore, the results showed that an appropriate concentration of Cu2+ helped to promote the thermal stability of laccase during the enzymatic reaction. This study could help researchers to avoid the use of inhibitory exogenous metal ions and anions in the application of laccase and to maximize the value of laccase.