Spectroscopic studies of the type 2 and type 3 copper centres in the mercury derivative of laccase.
U.v.-visible-absorption and e.p.r. spectroscopy were used to study the type 2 and type 3 copper centres in the mercury derivative of laccase. After treatment with peroxide the mercury derivative of laccase exhibits a fully developed absorption band at 330 nm (delta epsilon = 2900 +/- 100 M-1.cm-1, which is characteristic of type 3 copper in the oxidized state. In addition, there is a weak ligand-field absorption at 740 nm (epsilon = 380 +/- 30 M-1.cm-1), which can be assigned to the type 3 pair. Because the e.p.r. spectrum of the type 2 copper is well resolved in the case of the mercury derivative of laccase, for the first time we have been able to observe spectroscopic evidence for a pH-dependent structural transition that has been invoked to explain the kinetics of enzyme reduction [Andréasson & Reinhammar (1979) Biochim. Biophys. Acta 568, 145-156]. According to the e.p.r. data the pKa lies in the range 6-7, and comparisons with a model compound show that the spectral changes can plausibly be interpreted in terms of the deprotonation of a water molecule in the co-ordination sphere of the type 2 copper.
Tamilarasan
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Department of Chemistry, Purdue University, West Lafayette, IN 47907-3699.
McMillin
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D003300:Copper; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D042845:Laccase; D008628:Mercury; D010084:Oxidation-Reduction; D010088:Oxidoreductases; D010545:Peroxides; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet; D013057:Spectrum Analysis
D010545:Peroxides; D003300:Copper; D010088:Oxidoreductases; D042845:Laccase; D008628:Mercury