The Electronic Structure of the H-Cluster in the [FeFe]-Hydrogenase from Desulfovibrio desulfuricans: A Q-band 57Fe-ENDOR and HYSCORE Study

详细信息    查看全文

• 作者：Alexey Silakov ; Eduard J. Reijerse ; Simon P. J. Albracht ; E. Claude Hatchikian ; Wolfgang Lubitz
• 刊名：Journal of the American Chemical Society
• 出版年：2007
• 出版时间：September 19, 2007
• 年：2007
• 卷：129
• 期：37
• 页码：11447 - 11458
• 全文大小：566K
• 年卷期：v.129,no.37(September 19, 2007)
• ISSN：1520-5126

文摘

The active site of the P>57Fe-enriched [FeFe]-hydrogenase (i.e., the "H-cluster") from Desulfovibriodesulfuricans has been examined using advanced pulse EPR methods at X- and Q-band frequencies.For both the active oxidized state (H_ox) and the CO inhibited form (H_ox-CO) all six ⁵⁷Fe hyperfine couplingswere detected. The analysis shows that the apparent spin density extends over the whole H-cluster. Theinvestigations revealed different hyperfine couplings of all six ⁵⁷Fe nuclei in the H-cluster of the H_ox-COstate. Four large ⁵⁷Fe hyperfine couplings in the range 20-40 MHz were found (using pulse ENDOR andTRIPLE methods) and were assigned to the [4Fe-4S]_H (cubane) subcluster. Two weak ⁵⁷Fe hyperfinecouplings below 5 MHz were identified using Q-band HYSCORE spectroscopy and were assigned to the[2Fe]_H subcluster. For the H_ox state only two different ⁵⁷Fe hyperfine couplings in the range 10-13 MHzwere detected using pulse ENDOR. An ⁵⁷Fe line broadening analysis of the X-band CW EPR spectrumindicated, however, that all six ⁵⁷Fe nuclei in the H-cluster are contributing to the hyperfine pattern. It isconcluded that in both states the binuclear subcluster [2Fe]_H assumes a [Fe^IFe^II] redox configuration wherethe paramagnetic Fe^I atom is attached to the [4Fe-4S]_H subcluster. The ⁵⁷Fe hyperfine interactions of theformally diamagnetic [4Fe-4S]_H are due to an exchange interaction between the two subclusters as hasbeen discussed earlier by Popescu and Münck [Popescu, C.V.; Münck, E., J. Am. Chem. Soc. 1999, 121,7877-7884]. This exchange coupling is strongly enhanced by binding of the extrinsic CO ligand. Bindingof the dihydrogen substrate may induce a similar effect, and it is therefore proposed that the observedmodulation of the electronic structure by the changing ligand surrounding plays an important role in thecatalytic mechanism of [FeFe]-hydrogenase.