期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2004
卷号：101
期号：30
页码：10913-10918
DOI：10.1073/pnas.0402711101
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The all-ferrous Rieske cluster, [2Fe-2S]0, has been produced in solution and characterized by protein-film voltammetry and UV-visible, EPR, and Mossbauer spectroscopies. The [2Fe-2S]0 cluster, in the overexpressed soluble domain of the Rieske protein from the bovine cytochrome bc1 complex, is formed at -0.73 V at pH 7. Therefore, at pH 7, the [2Fe-2S]1+/0 couple is 1.0 V below the [2Fe-2S]2+/1+ couple. The two cluster-bound ferrous irons are both high spin (S = 2), and they are coupled antiferromagnetically (-J [≥] 30 cm-1, H =-2JS1{middle dot}S2) to give a diamagnetic (S = 0) ground state. The ability of the Rieske cluster to exist in three oxidation states (2+, 1+, and 0) without an accompanying coupled reaction, such as a conformational change or protonation, is highly unusual. However, uncoupled reduction to the [2Fe-2S]0 state occurs at pH > 9.8 only, and at high pH the intact cluster persists in solution for <1 min. At pH < 9.8, the all-ferrous cluster is stabilized significantly by protonation. A combination of experimental data and calculations based on density functional theory suggests strongly that the proton binds to one of the cluster {micro}2-sulfides, consistent with observations that reduced [3Fe-4S] clusters are protonated also. The implications for our understanding of coupled reactions at iron-sulfur clusters and of the factors that determine the relative stabilities of their different oxidation states are discussed.
