The Rieske iron-sulfur (Fe-S) cluster is a catalytic subunit of the mitochondrial cytochrome bc1 complex critical in ATP synthesis. The cluster accepts an electron and a proton when the mobile electron carrier, ubiquinol, is oxidized at the Qi site. The Fe-S cluster is believed to accept the first electron and , the mechanism of proton coupled electron transfer is dependent on the protonation states of the histidine ligands to one of the Fe-S cluster's iron atoms. Optimized geometries for the Fe-S cluster were generated and frequency analyses were performed for different protonation states of the imidazole side chains of histidine. Multiple large 15N isotopic vibrational frequency shifts are calculated for the protonated imidazole ligand but not in the deprotonated form. This method presents a possible approach for the experimental determination of the protonation states of the ligands by means of vibrational spectroscopy.

<sup>15</sup>N vibrational frequency shifts of the cytochrome bc1 Reiske Iron-Sulfur Cluster distinguishes the protonation states of the imidazole side chains of histidine ligands

247th National Meeting (2014)

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15N vibrational frequency shifts of the cytochrome bc1 Reiske Iron-Sulfur Cluster distinguishes the protonation states of the imidazole side chains of histidine ligands

¹⁵N vibrational frequency shifts of the cytochrome bc1 Reiske Iron-Sulfur Cluster distinguishes the protonation states of the imidazole side chains of histidine ligands