The 1H nuclear-magnetic-resonance spectroscopy of cobalt(II)-β-lactamase II

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Abstract
The 1H NMR spectra of [Bacillus cereus] .beta.-lactamase II in the presence of Co(II) were studied. Analysis of the spectra suggests that Co(II) binds at the same 2 metal-binding sites as does Zn(II). The binding of Co(II) at the 1st site is much weaker than the binding of Zn(II) at this site, whereas the binding of Co(II) at the 2nd site is tighter than the binding of Zn(II). The binding of Co(II) to the mono-zinc(II)-enzyme caused only 1 marked change in the spectrum, namely a decrease in the intensity of the resonances assigned to the C-2 and C-4 protons of one histidine residue (residue E). 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 1st metal-ion-binding site (where the ligands are the enzyme''s sole thiol gro and 3 histidine residues). This may be because the 1st site is internal, or beca use of a difference in conformation between the apoenzyme and the mono-Co(II)-enzyme. The 2nd site may be located on the surface of the molecule.