Zn(II) Dependence of the Aeromonas hydrophila AE036 Metallo-beta-lactamase Activity and Stability Hernandez-Valladares, María Felici, Antonio Weber, Georges Adolph, Hans Werner Zeppezauer, Michael Rossolini, Gian Maria Amicosante, Gianfranco Frere, Jean Marie Galleni, Moreno Aeromonas Metallo-beta-lactamase Activity Bidistilled water was kindly provided by Pr. E. Merciny from the Analytical Chemistry Department. We thank Dr. Jean-Marie François and Etienne Baise for helpful discussion of the microcalorimetric data. We also thank the Laboratoires Santé et Environnement, Institut E. Malvoz of Province de Liège, for the ICPMS measurements. The purchase of the microcalorimeter was financed by a grant from the Fonds National de la Recherche Scientifique (Brussels, Belgium; Contract No. 94551.94) Two Zn2+ binding sites were found in the Aeromonas hydrophila AE036 metallo-β-lactamase. The affinity of the first binding site for Zn2+ ions is so high that the dissociation constant could not be determined, but it is significantly lower than 20 nM. The mono-Zn2+ form of the enzyme exhibits a maximum activity against its carbapenem substrates. The presence of a Zn2+ ion in the second lower affinity binding site results in a loss of enzymatic activity with a Ki value of 46 μM at pH 6.5. The kinetic analysis is in agreement with a noncompetitive inhibition mechanism. The Zn content of the A. hydrophila enzyme is also strongly pH-dependent. With an external Zn2+ ion concentration of 0.4 μM, occupancy of the higher affinity site by metal ions is lower than 10% at pH 5 and 10. The affinity for the second binding site seems to increase from pH 6 to 7.5. Fluorescence emission and circular dichroism spectra revealed slight conformational changes upon titration of the apoenzyme by Zn2+ ions, resulting in the successive saturation of the first and second binding sites. Differential scanning calorimetry transitions and intrinsic fluorescence emission spectra in the presence of increasing concentrations of urea demonstrate that the catalytic zinc strongly stabilizes the conformation of the enzyme whereas the di-Zn enzyme is even more resistant to thermal and urea denaturation than the mono-Zn enzyme. The Zn2+ dependency of the activity of this metallo-β-lactamase thus appears to be very different from that of the homologous Bacteroides fragilis enzyme for which the presence of two Zn2+ ions per molecule of protein appears to result in maximum activity. 2026-01-07T11:30:28Z 2026-01-07T11:30:28Z 1997-09-23 journal article Hernandez Valladares, M., Felici, A., Weber, G., Adolph, H. W., Zeppezauer, M., Rossolini, G. M., Amicosante, G., Frère, J. M., & Galleni, M. (1997). Zn(II) dependence of the Aeromonas hydrophila AE036 metallo-beta-lactamase activity and stability. Biochemistry, 36(38), 11534–11541. https://doi.org/10.1021/bi971056h 0006-2960 1520-4995 https://hdl.handle.net/10481/109249 10.1021/bi971056h eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional American Chemical Society