1H NMR and UV-Vis spectroscopic characterization of sulfonamide complexes of nickel(II)-carbonic anhydrase. Resonance assignments based on NOE effects.

The binding of acetazolamide, p-fluorobenzensulfonamide, p-toluenesulfonamide, and sulfanilamide to nickel(II)-substituted carbonic anhydrase II has been studied by 1H NMR and electronic absorption spectroscopies. These inhibitors bind to the metal ion forming 1:1 complexes and their affinity constants were determined. The 1H NMR spectra of the formed complexes show a number of isotropically shifted signals corresponding to the histidine ligands. The complexes with benzene-sulfonamides gave rise to very similar 1H NMR spectra. The NMR data suggest that these aromatic sulfonamides bind to the metal ion altering its coordination sphere. In addition, from the temperature dependence of 1H NMR spectra of the p-fluorobenzenesulfonamide adduct, a conformational change is suggested. The T1 values of the meta-like protons of the coordinated histidines have been measured and resonance assignments based on NOE experiments were performed.