Dynamics of Mononuclear Cadmium β-Lactamase Revealed by the Combination of NMR and PAC Spectroscopy

Citations Over TimeTop 10% of 2001 papers

Abstract

The two metal sites in cadmium substituted beta-lactamase from Bacillus cereus 569/H/9 have been studied by NMR spectroscopy ((1)H, (15)N, and (113)Cd) and PAC spectroscopy ((111m)Cd). Distinct NMR signals from the backbone amides are identified for the apoenzyme and the mononuclear and binuclear cadmium enzymes. For the binuclear cadmium enzyme, two (113)Cd NMR signals (142 and 262 ppm) and two (111m)Cd PAC nuclear quadrupole interactions are observed. Two nuclear quadrupole interactions are also observed, with approximately equal occupancy, in the PAC spectra at cadmium/enzyme ratios < 1; these are different from those derived for the binuclear cadmium enzyme, demonstrating interaction between the two metal ion binding sites. In contrast to the observation from PAC spectroscopy, only one (113)Cd NMR signal (176 ppm) is observed at cadmium/enzyme ratios < 1. The titration of the metal site imidazole (N)H proton signals as a function of cadmium ion-to-enzyme ratio shows that signals characteristic for the binuclear cadmium enzyme appear when the cadmium ion-to-enzyme ratio is between 1 and 2, whereas no signals are observed at stoichiometries less than 1. The simplest explanation consistent with all data is that, at cadmium/enzyme ratios < 1, the single Cd(II) is undergoing exchange between the two metal sites on the enzyme. This exchange must be fast on the (113)Cd NMR time scale and slow on the (111m)Cd PAC time scale and must thus occur in a time regime between 0.1 and 10 micros.

Related Papers

• A GEOMETRIC MEAN IN THE FURUTA INEQUALITY(2002)
• Susquehanna Chorale Spring Concert "Roots and Wings"(2017)
• Коммуникaтивно- прaгмaтический aнaлиз дипломaтических бумaг (нa основе вербaльных нот)(2018)
• → ФОРМИРОВAНИЕ ГОТОВНОСТИ БУДУЩИХ ПЕДAГОГОВ К ОРГAНИЗAЦИИ РAБОТЫ ПО РAЗВИТИЮ ВAЛЕОЛОГИЧЕСКОЙ КУЛЬТУРЫ ШКОЛЬНИКОВ(2023)