| Autor: |
Henthorn JT; Max Planck Institute for Chemical Energy Conversion , Stiftstr. 34-36 , D-45470 Mülheim an der Ruhr , Germany., Arias RJ; Division of Chemistry and Chemical Engineering , California Institute of Technology , Pasadena , California 91125 , United States., Koroidov S; PULSE Institute , SLAC National Accelerator Laboratory , Menlo Park , California 94025 , United States., Kroll T; Stanford Synchrotron Radiation Lightsource , SLAC National Accelerator Laboratory , Menlo Park , California 94025 , United States., Sokaras D; Stanford Synchrotron Radiation Lightsource , SLAC National Accelerator Laboratory , Menlo Park , California 94025 , United States., Bergmann U; PULSE Institute , SLAC National Accelerator Laboratory , Menlo Park , California 94025 , United States., Rees DC; Division of Chemistry and Chemical Engineering , California Institute of Technology , Pasadena , California 91125 , United States.; Howard Hughes Medical Institute , California Institute of Technology , Pasadena , California 91125 , United States., DeBeer S; Max Planck Institute for Chemical Energy Conversion , Stiftstr. 34-36 , D-45470 Mülheim an der Ruhr , Germany. |
| Abstrakt: |
The size and complexity of Mo-dependent nitrogenase, a multicomponent enzyme capable of reducing dinitrogen to ammonia, have made a detailed understanding of the FeMo cofactor (FeMoco) active site electronic structure an ongoing challenge. Selective substitution of sulfur by selenium in FeMoco affords a unique probe wherein local Fe-Se interactions can be directly interrogated via high-energy resolution fluorescence detected X-ray absorption spectroscopic (HERFD XAS) and extended X-ray absorption fine structure (EXAFS) studies. These studies reveal a significant asymmetry in the electronic distribution of the FeMoco, suggesting a more localized electronic structure picture than is typically assumed for iron-sulfur clusters. Supported by experimental small molecule model data in combination with time dependent density functional theory (TDDFT) calculations, the HERFD XAS data is consistent with an assignment of Fe2/Fe6 as an antiferromagnetically coupled diferric pair. HERFD XAS and EXAFS have also been applied to Se-substituted CO-inhibited MoFe protein, demonstrating the ability of these methods to reveal electronic and structural changes that occur upon substrate binding. These results emphasize the utility of Se HERFD XAS and EXAFS for selectively probing the local electronic and geometric structure of FeMoco. |
