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| Content Provider | World Health Organization (WHO)-Global Index Medicus |
|---|---|
| Author | Dean, Dennis R. Hoffman, Brian M. Seefeldt, Lance C. Lukoyanov, Dmitriy Barney, Brett M. |
| Description | Author Affiliation: Lukoyanov D ( Department of Chemistry, Northwestern University, Evanston, IL 60208, USA.); |
| Abstract | A major obstacle to understanding the reduction of N2 to NH3 by nitrogenase has been the impossibility of synchronizing electron delivery to the MoFe protein for generation of specific enzymatic intermediates. When an intermediate is trapped without synchronous electron delivery, the number of electrons, n, it has accumulated is unknown. Consequently, the intermediate is untethered from kinetic schemes for reduction, which are indexed by n. We show that a trapped intermediate itself provides a 'synchronously prepared' initial state, and its relaxation to the resting state at 253 K, conditions that prevent electron delivery to MoFe protein, can be analyzed to reveal n and the nature of the relaxation reactions. The approach is applied to the 'H+/H- intermediate' (A) that appears during turnover both in the presence and absence of N2 substrate. A exhibits an S = 1/2 EPR signal from the active-site iron-molybdenum cofactor (FeMo-co) to which are bound at least two hydrides/protons. A undergoes two-step relaxation to the resting state (C): A --> B --> C, where B has an S = 3/2 FeMo-co. Both steps show large solvent kinetic isotope effects: KIE approximately 3-4 (85% D2O). In the context of the Lowe-Thorneley kinetic scheme for N2 reduction, these results provide powerful evidence that H2 is formed in both relaxation steps, that A is the catalytically central state that is activated for N2 binding by the accumulation of n = 4 electrons, and that B has accumulated n = 2 electrons. |
| ISSN | 00278424 |
| e-ISSN | 10916490 |
| Journal | Proceedings of the National Academy of Sciences of the United States of America |
| Issue Number | 5 |
| Volume Number | 104 |
| Language | English |
| Publisher | National Academy of Sciences |
| Publisher Date | 2007-01-01 |
| Publisher Place | United States |
| Access Restriction | Open |
| Subject Keyword | Azotobacter Vinelandii Enzymology Biochemistry Molybdoferredoxin Chemistry Nitrogen Nitrogenase Electron Spin Resonance Spectroscopy Electrons Hydrogen-Ion Concentration Kinetics Models, Chemical Protein Binding Protons Substrate Specificity Research Support, N.I.H., Extramural Research Support, U.S. Gov't, Non-P.H.S. Multidisciplinary |
| Content Type | Text |
| Resource Type | Article |
| Subject | Multidisciplinary |
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