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Distinguishing Protonation States of Histidine Ligands to the Oxidized Rieske Iron–Sulfur Cluster through 15 N Vibrational Frequency Shifts
Author(s) -
Jagger Benjamin R.,
Koval Ashlyn M.,
Wheeler Ralph A.
Publication year - 2016
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201500838
Subject(s) - protonation , chemistry , cluster (spacecraft) , iron–sulfur cluster , sulfur , histidine , inorganic chemistry , crystallography , computational chemistry , photochemistry , ion , organic chemistry , enzyme , computer science , programming language
Abstract The Rieske [2Fe–2S] cluster is a vital component of many oxidoreductases, including mitochondrial cytochrome bc1; its chloroplast equivalent, cytochrome b6f; one class of dioxygenases; and arsenite oxidase. The Rieske cluster acts as an electron shuttle and its reduction is believed to couple with protonation of one of the cluster′s His ligands. In cytochromes bc1 and b6f, for example, the Rieske cluster acts as the first electron acceptor in a modified Q cycle. The protonation states of the cluster′s His ligands determine its ability to accept a proton and possibly an electron through a hydrogen bond to the electron carrier, ubiquinol. Experimental determination of the protonation states of a Rieske cluster′s two His ligands by NMR spectroscopy is difficult, due to the close proximity of the two paramagnetic iron atoms of the cluster. Therefore, this work reports density functional calculations and proposes that difference vibrational spectroscopy with 15 N isotopic substitution may be used to assign the protonation states of the His ligands of the oxidized Rieske [2Fe–2S] complex.