The Effect of Fluoride on the Spectral and Catalytic Properties of Three Copper‐Containing Oxidases

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Abstract
The optical spectra of fungal laccase, lacquer tree laccase and ceruloplasmin are changed in a similar way when F– is added to the proteins at pH 5.5. A change around 320 nm is associated with the binding of F– to type 2 Cu2+ of the proteins as seen from a correlation with electron paramagnetic resonance spectra. The rate of binding of F– to fungal laccase is first order with respect to uncomplexed enzyme and independent of the F– concentration, indicating that an intramolecular process is rate limiting. The stability constant of the enzyme · F– complex is greater than 10 μM‐1. Fungal laccase is almost completely inhibited when 1 equivalent of F– is bound to the type 2 Cu2+. Presence of substrate gradually decreases the inhibition, due to the release of F– from a reduced form of the enzyme.