EVIDENCE FOR TEMPERATURE-DEPENDENT CHANGES IN THE COUPLING WITHIN THE TYPE-2 TYPE-3 CLUSTER OF LACCASE

The type 2 depleted form of isotopically enriched laccase has been prepared and subsequently reconstituted with a different copper isotope. The results indicate that the copper ion which is removed and reinserted is not the same copper ion that is responsible for the type 2 EPR signal observed at low temperature. However, S-band EPR data show that the reactive copper center is EPR active at room temperature. These findings are explained in terms of a temperature-dependent structural reorganization and a change in the nature of the antiferromagnetic coupling that occurs within the type 2/type 3 cluster of laccase. This phenomenon may be connected with a previously identified conformational transition of the enzyme.