首页 | 本学科首页   官方微博 | 高级检索  
   检索      


Redox potential changes during ATP‐dependent corrinoid reduction determined by redox titrations with europium(II)–DTPA
Authors:Hendrike Dürichen  Gabriele Diekert  Sandra Studenik
Abstract:Corrinoids are essential cofactors of enzymes involved in the C1 metabolism of anaerobes. The active, super‐reduced CoI] state of the corrinoid cofactor is highly sensitive to autoxidation. In O‐demethylases, the oxidation to inactive CoII] is reversed by an ATP‐dependent electron transfer catalyzed by the activating enzyme (AE). The redox potential changes of the corrinoid cofactor, which occur during this reaction, were studied by potentiometric titration coupled to UV/visible spectroscopy. By applying europium(II)–diethylenetriaminepentaacetic acid (DTPA) as a reductant, we were able to determine the midpoint potential of the CoII]/CoI] couple of the protein‐bound corrinoid cofactor in the absence and presence of AE and/or ATP. The data revealed that the transfer of electrons from a physiological donor to the corrinoid as the electron‐accepting site is achieved by increasing the potential of the corrinoid cofactor from ?530 ± 15 mV to ?250 ± 10 mV (ESHE, pH 7.5). The first 50 to 100 mV of the shift of the redox potential seem to be caused by the interaction of nucleotide‐bound AE with the corrinoid protein or its cofactor. The remaining 150–200 mV had to be overcome by the chemical energy of ATP hydrolysis. The experiments revealed that Eu(II)–DTPA, which was already known as a powerful reducing agent, is a suitable electron donor for titration experiments of low‐potential redox centers. Furthermore, the results of this study will contribute to the understanding of thermodynamically unfavorable electron transfer processes driven by the power of ATP hydrolysis.
Keywords:ATP‐dependent corrinoid reduction  corrinoid cofactor  europium     O‐demethylase  potentiometric titration  thermodynamically unfavorable electron transfer
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号