X-ray-absorption Studies On Catechol 2,3-dioxygenase From Pseudomonas-putida Mt2

X-ray absorption spectroscopy has been utilized to investigate the structure of the active site of iron(II) catechol 2,3-dioxygenase from Pseudomonas putida mt2 both in the native and the 2-chlorophenol inhibited forms. XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) results allow us to discuss the coordination number and geometry of the ferrous ion in the native enzyme. The metal geometry is not significantly affected by the binding of the inhibitor. The EXAFS spectrum is consistent with an iron(II) bound to six N/O atoms at an average distance of 2.05 Angstrom or to five N/O at an average distance of 2.04 Angstrom. The simulation of the experimental data is greatly enhanced by considering the iron ligands divided in two different shells. Analysis of the outer shells performed using multiple scattering theory shows that there are histidines in the coordination sphere. The best fitting is obtained assuming the presence of two of them. Similar results are obtained for the inhibited enzyme, which, however, are indicative of a slight shortening of the average metal-donor bond distances. The direct binding of inhibitors to the metal center is confirmed by H-1 NMR data.