The mechanism of electron transfer in laccase-catalysed reactions

1. The reaction of the electron acceptors in Rhus vernicifera laccase (monophenol, dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1) have been studied with stopped-flow and rapid-freeze EPR techniques. The studies have been directed mainly towards elucidation of the role of the type 2Cu2+ as a possible pH-sensitve regulator of electron transfer. 2. Anaerobic reduction experiments with Rhus laccase indicate that the type 1 and 2 sites contribute one electron each to the reduction of the two-electron-accepting type 3 site. There is also evidence that the reduction of the type 1 Cu2+ triggers the reduction of the type 2 Cu2+. 3. Only at pH values at which the reduction of the two-electron acceptor is limited by a slow intramolecular reaction can an OH- be displaced from the type 2 Cu2+ by the inhibitor F-. 4. A model describing the role of the electron-accepting sites in catalysis is formulated.