Two-dimensional 1H-NMR spectra were carried out on bovine Cu(I),Zn Superoxide dismutase. The ring protons of the single tyrosine and of the 4 phenylalanines were identified from COSY spectra. Prom NOESY spectra all imidazole C-resonances could be specifically assigned to each of the 8 histidines using the crystal coordinates of the Cu(II),Zn enzyme. Since 6 histidines are involved in the structure of the active site, this result implies nearly identical active site conformations for the two oxidation states of the catalytic cycle of this enzyme, in line with its diffusion-limited rate.
