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The ' H Nuclear-Magnetic-Resonance Spectroscopy of Cobalt ( II )-P-Lactamase II

The 'H n.m.r. spectra of ,6-lactamase II in the presence of Co(II) were studied. Analysis of the spectra suggests that Co(II) binds at the same two metal-binding sites as does Zn(II). The binding of Co(II) at the first site is much weaker than the binding of Zn(II) at this site, whereas the binding of Co(II) at the second site is tighter than the binding of Zn(II). The binding of Co(II) to the mono-zinc(II)-enzyme caused only one marked change in the spectrum, namely a decrease in the intensity of the resonances assigned to the C-2 and C4 protons of one histidine residue (residue E). However, when the spectra of the apoenzyme and the Co(II)-enzyme were compared, there were many differences. A significant fraction of the protons in the whole molecule are affected by the binding of Co(II) at the first metal-ion-binding site (where the ligands are the enzyme's sole thiol group and three histidine residues). This may be because the first site is internal, or because of a difference in conformation between the apoenzyme and the monoCo(II)-enzyme. The second site may be located on the surface of the molecule.