| Abstract: | 1. In anaerobic reduction studies on fungal laccase B (p-diphenol:O2 oxidoreductase, EC 1.14.18.1) with the EPR and stopped-flow techniques it was found that the type 2 copper of the enzyme is rapidly undergoing a reduction-oxidation cycle which is followed by a slower reduction in a couple of seconds. An intermediate EPR signal of unknown origin is formed in the same time-range as the initial reduction of type 2 copper and disappears again when this copper ion is reoxidized. 2. The rate of the anaerobic reoxidation of type 2 copper is similar to the reduction rate of the two-electron acceptor, suggesting that they are interacting in the electron transfer of the enzyme. 3. The changes in the reaction rates of both type 2 and type 3 copper appear to be affected in a similar way by changes in pH. 4. The EPR signal of the type 2 Cu2+ suggests that this ion is liganded to one or more nitrogens. |
