The 1H-NMR relaxation of Rhus laccase: assignment to different types of copper

1H-NMR relaxation measurements of Rhus laccase showed that a portion of the relaxivity was specifically abolished by less than stoichiometric EDTA. Another portion of relaxivity was removed by addition of N3(-) to the EDTA saturated enzyme. This treatment or selective removal of the Type 2 Cu left a large residual paramagnetic relaxivity (1700 M-1s-1) which was assigned to the Type 1 Cu. It is concluded that only a portion of the laccase relaxivity can be assigned to the Type 1 Cu and that this copper type does not behave homogeneously: the two fractions have different relaxivity, 5200 and less than or equal to 2400 M-1s-1 respectively.