The Kinetics of the Anaerobic Reduction of Fungal Laccase B

Abstract

1 A stopped-flow technique was used to study the anaerobic reduction of fungal laccase B by hydroquinone, ascorbate and Fe(CN)64-. The reactions were followed by measurements of the intensity of absorption bands at 610 and 330 nm, related to a one- and a two-electron acceptor, respectively. 2 The experiments confirmed earlier results indicating a second-order reduction of the 610-nm chromophore. The reduction of the 330-nm chromophore was found to be consistent with the concept that the rate is limited by an intramolecular step. A model for the anaerobic reduction of laccase was formulated. 3 The effect of F− on the anaerobic kinetics implies that this inhibitory anion changes the rate constant of the rate-limiting step. 4 The reduction of the 330-nm chromophore, as it appears under anaerobic conditions, cannot be part of the normal catalytic mechanism.