The phenoloxidases of the ascomycete Podospora anserina XI. The state of copper of laccases I, II and III

Abstract

1. 1. Laccases I, II and III were (EC 1.14.18.1) prepared from the mycelium of the ascomycete Podospora anserina. The tetrameric laccase I (mol. wt 340 000, 16 copper atoms) and the monomeric laccases II and III (mol. wt 80 000, 4 copper atoms) have been studied by optical absorption-, circular dichroism-(CD) and electron paramagnetic resonance spectroscopy (EPR). 2. 2. The visible and near ultraviolet difference absorption spectrum, which is apparently identical for all three laccases, shows two maxima at 330 and 610 nm and a shoulder at about 725 nm. The molar extinction coefficients of these bands are 4 times larger for the tetrameric laccase I compared to the monomeric laccases II and III which show values similar to other blue copper-containing oxidases. 3. 3. CD spectra between 300 and 730 nm of the tree laccases are similar and contain at least 5-bands in the oxidized enzyme. If the enzyme is reduced, only a band at 307 nm remains. The molar ellipticity values of these bands are 4 times larger for laccase I than the corresponding bands of laccases II and III. It is inferred that the reducible bands are associated with the Type 1 Cu 2+. 4. 4. In all three laccases the EPR-detectable copper accounts for only about 50% of the total copper content. The 9-GHz and 35-GHz spectra, which are identical for all three laccases, consist of two components of equal intensity. One component shows a rather small copper hyperfine coupling and a small deviation from axial symmetry. It is suggested that this copper is associated with the blue chromophore in analogy to Type 1 Cu 2+ in other blue copper proteins. The other component has a broader hyperfine coupling similar to Type 2 Cu 2+ as found in other copper proteins. The assumption that the experimental spectra result from a superposition of the spectra of equal amounts of Type 1 and Type 2 Cu 2+ has been verified by computer simulation. 5. 5. It is suggested that the copper ions which are not detected by EPR are connected to the absorption band at 330 nm and that these ions are also essential for the function of these laccases.