Binding Sites of Nitrogenase: Kinetic and Theoretical Studies of Cyanide Binding to Extracted FeMo-Cofactor Derivatives

详细信息    查看全文

• 作者：Zhen Cui ; Adrian J. Dunford ; Marcus C. Durrant ; Richard A. Henderson ; and Barry E. Smith
• 刊名：Inorganic Chemistry
• 出版年：2003
• 出版时间：October 6, 2003
• 年：2003
• 卷：42
• 期：20
• 页码：6252 - 6264
• 全文大小：206K
• 年卷期：v.42,no.20(October 6, 2003)
• ISSN：1520-510X

文摘

The first kinetic study of a substrate (CN^-) binding to the isolated active site (extracted FeMo-cofactor) of nitrogenaseis 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 therate of the reaction of the cofactor with PhS^-. The kinetic results, together with DFT calculations, indicate that theinitial site of CN^- binding to FeMoco-L is controlled by a combination of the electron-richness of the cluster coreand lability of the Mo-L bond. Ultimately, the reactions between FeMoco-L and CN^- involve displacement of Land binding of CN^- to Mo. These reactions occur with a variety of rates and rate laws dependent on the natureof L. For FeMoco-NMF, the reaction with CN^- is complete within the dead-time of the apparatus (ca. 4 ms), whilewith FeMoco-CNBu^t the reaction is much slower and exhibits first order dependences on the concentrations ofboth FeMoco-CNBu^t 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 concentrationof 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-CNBu^t initial binding at an Fe site is followed by movement of CN^- toMo. Complementary DFT calculations are consistent with this interpretation, indicating that, in FeMoco-L, theMo-L bond is stronger for L = ImH than for L = CNBu^t and the binding of CN^- to Mo is stronger than to any Featom in the cofactor.