Electron--nuclear-double-resonance studies of spinach plastocyanin

Electron--nuclear-double-resonance (ENDOR) studies of spinach plastocyanin revealed that 14N-hyperfine couplings from its two co-ordinated imidazole groups are characteristically small in anisotropy and relatively high in ENDOR frequencies and that the two imidazole groups are magnetically equivalent. The relatively strong copper-imidazole co-ordinate bonds of plastocyanin are interpreted to be a result of the coexistence of a strong copper--thiol co-ordinate bond.