ePrints

Binding sites of nitrogenase: Kinetic and theoretical studies of cyanide binding to extracted FeMo-cofactor derivatives

Lookup NU author(s): Adrain John Dunford, Professor Richard Henderson

Downloads

Full text for this publication is not currently held within this repository. Alternative links are provided below where available.

Abstract

The first kinetic study of a substrate (CN-) binding to the isolated active site (extracted FeMo-cofactor) of nitrogenase is described. The kinetics of the reactions between CN- and various derivatives of extracted FeMo-cofactor {FeMoco-L; where L is bound to Mo, and is NMF, Bu tNC, or imidazole (ImH)} have been followed using a stopped-flow, sequential-mix method in which the course of the reaction is followed indirectly, by monitoring the change in the rate of the reaction of the cofactor with PhS-. The kinetic results, together with DFT calculations, indicate that the initial site of CN- binding to FeMoco-L is controlled by a combination of the electron-richness of the cluster core and lability of the Mo-L bond. Ultimately, the reactions between FeMoco-L and CN- involve displacement of L and binding of CN- to Mo. These reactions occur with a variety of rates and rate laws dependent on the nature of L. For FeMoco-NMF, the reaction with CN- is complete within the dead-time of the apparatus (ca. 4 ms), while with FeMoco-CNBu t the reaction is much slower and exhibits first order dependences on the concentrations of both FeMoco-CNBut and CN- (k = 2.5 ± 0.5 × 104 dm3 mol-1 s -1). The reaction of FeMoco-ImH with CN- occurs at a rate which exhibits a first order dependence on FeMoco-ImH but is independent of the concentration of CN- (k = 50 ± 10 s-1). The results are interpreted in terms of CN- binding directly to the Mo site for FeMoco-NMF and FeMoco-ImH, but with FeMoco-CNBut initial binding at an Fe site is followed by movement of CN- to Mo. Complementary DFT calculations are consistent with this interpretation, indicating that, in FeMoco-L, the Mo-L bond is stronger for L = ImH than for L = CNBut and the binding of CN- to Mo is stronger than to any Fe atom in the cofactor.

Publication metadata

Author(s): Cui Z, Dunford AJ, Durrant MC, Henderson RA, Smith BE

Publication type: Article

Publication status: Published

Journal: Inorganic Chemistry

Year: 2003

Volume: 42

Issue: 20

Pages: 6252-6264

ISSN (print): 0020-1669

ISSN (electronic): 1520-510X

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/ic030108q

DOI: 10.1021/ic030108q

PubMed id: 14514300

Altmetrics

Share