title: EPR studies on the anaerobic reduction of fungal laccase. Evidence for participation of type 2 copper in the reduction mechanism.
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.
mesh_terms: D000693:Anaerobiosis; D001205:Ascorbic Acid; D001665:Binding Sites; D004156:Catechol Oxidase / Q000032:analysis; D003300:Copper / Q000032:analysis; D004578:Electron Spin Resonance Spectroscopy; D005658:Fungi / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D010636:Phenols; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D010636:Phenols; D003300:Copper; D004156:Catechol Oxidase; D001205:Ascorbic Acid