An epr signal from the half-reduced type 3 copper pair in Rhus vernicifera laccase

A new type of Cu(II) epr signals have been produced in native and type 2 copper depleted Rhus vernicifera laccase. They are shown to originate from one of the type 3 copper ions that are epr silent in the resting enzyme. The new epr signals show high rhombicity in g tensor and are similar to those observed in other proteins, such as superoxide dismutase and half-met hemocyanin. The half-reduced type 3 copper pair is formed by reduction with an electron from type 1 Cu(I) but only after a reoxidation of the copper pair, either by peroxide or dioxygen. It is suggested that the half-reduction of the type 3 copper pair only occurs in molecules where type 2 copper ion is either reduced or absent.