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| - EPR and Magnetic Susceptibility Studies of Cobalt(II)- and Nickel(II)-Substituted Azurinsfrom Pseudomonas aeruginosa. Electronic Structure of the Active Sites
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| - The electronic properties of cobalt(II)- andnickel(II)-substituted azurins from Pseudomonas aeruginosahavebeen investigated. EPR data for the cobalt derivative andparamagnetic susceptibility data for the nickel derivativeare reported. The EPR spectrum of Co(II)−azurin shows thetypical pattern of a Kramers' doublet (±1/2)associatedwith an S = 3/2 ground state in adistorted axial symmetry environment. The temperature dependenceof the EPRintensities shows that this Kramers' doublet is the excited doubletand, therefore, that the corresponding zero-field splitting parameter D is negative (∼−3.5cm-1). The mean g value isequal to 2.3. Nickel(II) azurin exhibitsan effective magnetic moment μeff = 2.8μB (Bohr magnetons), constant in the temperature range120−30 K.The magnetic moment decreases and reaches the value of 1.80μB at 5 K. From the temperature dependenceofthe susceptibility, the fitting of the data to the theoreticalS = 1 susceptibility equation leads to azero-fieldsplitting parameter D of around 17.7cm-1. The spin Hamiltonian parametersthat have been determined for thetwo metallosubstituted proteins are consistent with a highly distortedtetrahedral structure derived from an axiallyelongated trigonal bipyramid.
- EPR spectroscopy and paramagnetic susceptibility havebeen applied to study the electronic properties of cobalt(II)- andnickel(II)-substituted azurins from Pseudomonasaeruginosa for a better understanding of the metal site ofthese proteins in solution. The results are consistent with ahighly distorted tetrahedral environment of the active sites describedin a trigonal-bipyramidal geometry with one of the axial ligands movingaway from the metal center.
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