Magnetic studies of the trinuclear center in laccase and ascorbate oxidase approached by EPR spectroscopy and magnetic susceptibility measurements

" The trinuclear centers in Rhus uernicifera laccase and Cucumis sativus ascorbate oxidase have been studied by EPR spectroscopy and magnetic susceptibility measurements over the wide range of 5 K to 300 K. The EPR spectra showed that type 2 copper receives increasing tetrahedral distortion with raising temperature. Magnetic susceptibilities of laccase showed that both of type 1 and type 2 coppers are almost fully paramagnetic since the antiferromagnetic interaction between type 3 coppers is extremeely strong from 5 K to 300 K. On the other hand, the effective magnetic moment of ascorbate oxidase is contributed by ca. 1.7 Cu2+ even below ca. 100 K, since type 2 Cu is partly in the reduced from. The effective magnetic moment continuously increased with raising temperature because the antiferromagnetic interaction between type 3 coppers is not as strong as in the case of laccase. The simulation of the SQUID measurement results suggested that the conformational change of the ascorbate oxidase molecule caused the temperature dependence of the antiferromagnetic interaction."