Spinach plastocyanin: Comparison of reduced and oxidized forms by natural abundance carbon-13 nuclear magnetic resonance spectroscopy

Differences between the reduced Cu(I) and oxidized Cu(II) forms of spinach plastocyanin were investigated by natural abundance carbon-13 nuclear magnetic resonance spectroscopy at 67.9 MHz using proton noise decoupling. The spectra confirm that histidines 38 and 91 are copper ligands and demonstrate that coordination is by the N^o1 of both imidazole rings. Spectra of reduced plastocyanin yielded 128 separately resolved carbon resonances. Upon oxidation, 16 of these were observed to disappear; yet there was little change in the positions or intensities of other peaks. Those peaks which disappear are assigned to carbons near the metal. The protein evidently does not undergo a substantial change in conformation upon change of redox state.