The Rieske iron-sulfur cluster (2Fe-2S) is a catalytic subunit of the mitochondrial cytochrome bc1 complex critical in ATP synthesis. The cluster is proposed to act as both an electron and proton acceptor for the mobile electron carrier ubiquinol. Experimental data imply that the 2Fe-2S cluster can exist in three possible states during the oxidation-reduction process: oxidized-protonated, oxidized-deprotonated, and reduced-protonated. Optimized geometries for the 2Fe-2S cluster were generated and vibrational frequency analyses were performed for each of the three states.  Heisenberg Coupling Constant (J) values were also calculated and can be used to order the spin state energies for each state.  Large 15N isotopic shifts present a possible approach for the experimental determination of the protonation states of the ligands in the oxidized forms by means of difference IR spectroscopy. Comparisons between the oxidized and reduced forms of the cluster provide a more complete description of the electron transfer process.

Geometry optimizations and vibrational frequency analysis of the three possible states of the Rieske Iron-Sulfur Cluster

248th National Meeting (2014)

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