[Inhibition mechanism of Polyporus versicolor laccase by halide ions].

A kinetic study of inhibition of Polyporus versicolor laccase activity by fluoride-, chloride- and bromide ions has been carried out. It has been found that the fluoride ion is a non-competitive inhibitor with respect to the electron donor and a mixed inhibitor with respect to oxygen. However, the chloride and bromide ions are competitive inhibitors with respect to the electron donor. The constants of inhibition of the enzyme activity by both chloride and fluoride ions and the catalytic constant were found to be pH-dependent. Based on the pH-dependence of the catalytic constant, an existence of two ionogenic groups in the enzyme active site has been proposed. The existence of an alternative electron pathway in the enzyme active site is postulated. This pathway makes a noticeable contribution to the reaction rate when the concentration of the electron donor and the fluoride ion is high. This alternative electron pathway can be blocked by the chloride ions and the hydroxyl ions taken at high concentrations. A formal kinetic description of this phenomenon has been given and the role of the type 2 Cu2+ in the catalytic process has been evaluated.